NOAA Technical Memorandum GLERL-126

GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

I.J.C. LAKE ONTARIO-ST. LAWRENCE RIVER REGULATION STUDY

Thomas E. Croley II

NOAA, Great Lakes Environmental Research Laboratory, Ann Arbor, MI 48105

Great Lakes Environmental Research Laboratory

Ann Arbor, Michigan 

September 2003

UNITED STATES

DEPARTMENT OF COMMERCE

Donald Evans

Secretary

NATIONAL OCEANIC AND

ATMOSPHERIC ADMINISTRATION

Conrad C. Lautenbacher, Jr.

Administrator
NOTICE 

Mention of a commercial company or product does not constitute an endorsement 

by the NOAA. Use of information from this publication concerning proprietary 

products or the tests of such products for publicity or advertising purposes is not 

authorized. This is GLERL Contribution No. 1286.

This work was supported in part by funds from the International Joint Commission for their study of Lake Ontario—St. Lawrence River Regulation, administered by the Hydrology and Hydraulics Technical Working Group. 

This publication is available as a PDF file and can be downloaded from GLERL’s 

web site: www.glerl.noaa.gov. Hard copies can be requested from GLERL, Information services, 2205 Commonwealth Blvd., Ann Arbor, MI 48105. 

pubs.glerl@noaa.gov. 
 iii

TABLE OF CONTENTS 

LIST OF FIGURES .................................................................................................................. v 

LIST OF TABLES ...................................................................................................................vi 

ABSTRACT ............................................................................................................................vii

Project Rationale....................................................................................................................1 

Background .........................................................................................................................1 

Present Study ......................................................................................................................2 

Introduction.............................................................................................................................3 

Early Great Lakes Climate Change Impact Studies..........................................................3 

Recent Great Lakes Climate Change Impact Studies........................................................3 

GLERL-EPA 2xCO2 Impacts..........................................................................................3 

GLERL-IJC 2xCO2 Impacts............................................................................................4 

GCM Linkage Problems.....................................................................................................5 

Climate Transposition.........................................................................................................6 

US National Assessment of Climate Change in the Great Lakes ......................................7 

Present Study ......................................................................................................................8 

Great Lakes Dynamics and Climate ...................................................................................9 

Great Lakes Overview ........................................................................................................9 

Physical Processes............................................................................................................. 10 

Climatology ....................................................................................................................... 12 

Lake Level Fluctuation and Trends ................................................................................. 14 

Diversions.......................................................................................................................... 16 

Future ................................................................................................................................ 17 

Summary Comments on Great Lakes Dynamics............................................................. 18 

Methodology ......................................................................................................................... 19 

Climate Data...................................................................................................................... 19 

Changed Climate............................................................................................................... 20 

Great Lakes Physical Process Models ............................................................................ 23 

Runoff Modeling ............................................................................................................... 23 

Snowmelt and Infiltration.............................................................................................. 23 

Heat Available for Evapotranspiration........................................................................... 24 

Infiltration..................................................................................................................... 25 

Evapotranspiration ........................................................................................................ 25 

Mass Conservation ........................................................................................................ 26 

Analytical Solution........................................................................................................ 27 

Application.................................................................................................................... 27 

Calibration .................................................................................................................... 28 

Over-Lake Precipitation ................................................................................................... 30 
 iv

Over-Lake Evaporation .................................................................................................... 31 

Thermodynamic Fluxes................................................................................................. 32 

Heat Storage.................................................................................................................. 35 

Ice Pack Growth............................................................................................................ 37 

Calibration Procedure.................................................................................................... 38 

Application.................................................................................................................... 40 

Calibration Issues.......................................................................................................... 41 

Models Validity and Applicability.................................................................................... 42 

Great Lakes Climate Change Hydrological Responses ............................................... 45 

Basin Meteorology............................................................................................................. 45 

Basin Hydrology................................................................................................................ 47 

Over Water Meteorology .................................................................................................. 51 

Lake Heat Balance ............................................................................................................ 56 

Lake Thermal Structure ................................................................................................... 60 

Lake Water Balance.......................................................................................................... 61 

Hydrological Sensitivities .................................................................................................. 67 

Main Findings ................................................................................................................... 67 

Summary ........................................................................................................................... 68 

References ............................................................................................................................ 69 

Appendix – Notation............................................................................................................ 75 
 v

LIST OF FIGURES 

Figure 1. The Laurentian Great Lakes Basin............................................................................9 

Figure 2. Great Lakes Subbasin Mass Balance....................................................................... 11 

Figure 3. Lakes Michigan, Huron, St. Clair, and Erie 3-year-Mean Precipitation (1900-90)... 13 

Figure 4. Great Lakes Annual Air Temperature (1900-29, 1930-59, 1960-90) ....................... 14 

Figure 5. Lake Erie Seasonal Net Basin Supplies................................................................... 14 

Figure 6. Great Lakes Annual Water Levels (1900-90).......................................................... 15 

Figure 7. Lake Erie Annual Water Levels and Precipitation................................................... 15 

Figure 8. Average Seasonal Great Lakes Levels (1900-90).................................................... 16 

Figure 9. Lake Erie Seasonal Water Level Comparisons........................................................ 16 

Figure 10. Selected Great Lake Responses to Diversions ......................................................... 17 

Figure 11. Base Case Temperature and Precipitation Stations.................................................. 19 

Figure 12. Base Case Temperature, Humidity, Wind Speed, and Cloud Cover Stations ........... 19 

Figure 13. Conceptual Prismatic Ice Pack................................................................................ 35 

Figure 14. Lake Evaporation and Thermodynamics Model Conceptual Schematic................... 39 

Figure 15. Daily Average Air Temperature Averaged Over The Year...................................... 46 

Figure 16. Seasonal Lake Ontario Basin Average Meteorology and Hydrology ....................... 46 

Figure 17. Daily Total Precipitation Averaged Over The Year................................................. 47 

Figure 18. Daily Snow Water Equivalent Averaged Over The Year......................................... 49 

Figure 19. Daily Evapotranspiration Averaged Over The Year ................................................ 49 

Figure 20. Daily Soil Moisture Storage Averaged Over The Year............................................ 49 

Figure 21. Groundwater Storage Averaged Over The Year ...................................................... 49 

Figure 22. Daily Total Moisture Storage Averaged Over The Year.......................................... 50 

Figure 23. Daily Total Basin Runoff Averaged Over The Year................................................ 50 

Figure 24. Seasonal Lake Ontario Basin Average Moisture Storage......................................... 50 

Figure 25. Daily Surface Air Temperature Averaged Over The Year....................................... 54 

Figure 26. Daily Absolute Humidity Averaged Over The Year................................................ 54 

Figure 27. Daily Cloud Cover Averaged Over The Year.......................................................... 54 

Figure 28. Daily Average Wind Speed Averaged Over The Year............................................. 54 

Figure 29. Seasonal Lake Ontario Average Overlake Meteorology.......................................... 55 

Figure 30. Seasonal Lake Ontario Average Lake Heat Fluxes.................................................. 57 

Figure 31. Daily Surface Water Temperature Averaged Over The Year................................... 60 

Figure 32. Seasonal Lake Ontario Average Lake Heat Storage Characteristics ........................ 60 

Figure 33. Daily Evaporation Averaged Over The Year........................................................... 60 

Figure 34. Daily Precipitation Averaged Over The Year.......................................................... 62 

Figure 35. Daily Lake Runoff Averaged Over The Year ........................................................... 62 

Figure 36. Daily Net Basin Supply Averaged Over The Year .................................................. 63 

Figure 37. Seasonal Lake Ontario Average Net Basin Supply Components ............................. 63 
 vi

LIST OF TABLES 

Table 1. Laurentian Great Lake Size Statistics....................................................................... 10 

Table 2. Partial Great Lakes Annual Water Balance (1951-1988).......................................... 13 

Table 3. Great Lakes Annual Precipitation Summary ............................................................ 13 

Table 4. Impact of Existing Diversions on Lake Levels ......................................................... 17 

Table 5. Large Basin Runoff Model Parameters for the Lake Superior Subbasins.................. 29 

Table 6. Large Basin Runoff Model Parameters for the Lake Michigan Subbasins ................ 30 

Table 7. Large Basin Runoff Model Parameters for the Lake Huron Subbasins ..................... 30 

Table 8. Large Basin Runoff Model Parameters for the Georgian Bay Subbasins .................. 31 

Table 9. Large Basin Runoff Model Parameters for the Lake St. Clair Subbasins .................. 31 

Table 10. Large Basin Runoff Model Parameters for the Lake Erie Subbasins......................... 32 

Table 11. Large Basin Runoff Model Parameters for the Lake Ontario Subbasins ................... 32 

Table 12. Large Basin Runoff Model Calibration Statistics ..................................................... 33 

Table 13. Lake Evaporation and Thermodynamics Model Constants and Parameters .............. 40 

Table 14. Lake Evaporation and Thermodynamics Model Calibration Statistics ...................... 41 

Table 15. Average Annual Steady-State Basin Meteorology Differences................................. 45 

Table 16. Average Annual Steady-State Basin Meteorology Variability Differences ............... 46 

Table 17. Average Annual Steady-State Basin Hydrology Differences .................................... 48 

Table 18. Average Annual Steady-State Basin Hydrology Variability Differences .................. 52 

Table 19. Average Annual Steady-State Overlake Meteorology Differences ........................... 53 

Table 20. Average Annual Steady-State Overlake Meteorology Variability Differences.......... 55 

Table 21. Average Annual Steady-State Lake Heat Flux Differences ...................................... 56 

Table 22. Average Annual Steady-State Lake Heat Flux Variability Differences..................... 58 

Table 23. Average Annual Steady-State Lake Heat Balance Differences ................................. 59 

Table 24. Average Annual Steady-State Lake Heat Balance Variability Differences................ 61 

Table 25. Average Annual Steady-State Lake Water Balance Differences............................... 62 

Table 26. Average Annual Steady-State Lake Water Balance Variability Differences ............. 64 

Table 27. Average Annual Steady-State Great Lakes Basin Hydrology Summary ................... 66 
 vii

ABSTRACT 

Climatic change will impact on many aspects of the hydrological cycle with consequences for 

mankind that are interrelated and often difficult to discern. Climate warming will have impacts 

on Great Lakes water supply components and basin storages of water and heat that must be understood before lake level impacts can be assessed. Because the Laurentian Great Lakes possess 

tremendous water and heat storage capacities, they respond slowly to changed meteorological 

inputs. This memory damps short-term meteorological fluctuations, but allows response to 

longer-period fluctuations characteristic of climate change. Thus the large Great Lakes system is 

ideal for studying regional effects of climate changes. 

This project estimates hydrological impacts of changed climates over the Great Lakes from the 

latest general circulation model (GCM) results for the International Joint Commission’s five-year 

study of Lake Ontario—St. Lawrence regulation. This report concerns the US study of climate 

change performed by The Great Lakes Environmental Research Laboratory (GLERL). They extracted GCM output changes between a baseline period of 1961—1990 and a future 30-year period (2040—2069). GLERL adjusted historical meteorology data for the Great Lakes basin with 

the GCM climate changes. GLERL used a base climate (observed data) time series over 1950—

1999 to define the reference of 1960—1990 suggested by the Intergovernmental Panel on Climate Change. GLERL simulated Great Lakes hydrology to estimate net water supply scenarios 

for each lake under each climate scenario. 

This report provides background on earlier Great Lakes climate change impact studies, describes 

the Great Lakes and their climate, presents hydrological models used in assessing climate 

change, and summarizes results. Detailed time series of net basin supplies to all of the Great 

Lakes are available for an unchanged climate scenario and four GCM-generated changed-climate 

scenarios. 

The higher air temperatures under the changed-climate scenarios lead to higher over-land 

evapotranspiration and lower runoff to the lakes with earlier runoff peaks since snow pack is reduced and the snow season is greatly reduced. This also results in a reduction in available soil 

moisture. Water temperatures increase and peak earlier; heat resident in the deep lakes increases 

throughout the year. Mixing of the water column diminishes, as most of the lakes become 

mostly monomictic, and lake evaporation increases. Ice formation is greatly reduced over winter 

on the deep Great Lakes, and lake evaporation increases; average net supplies drop most where 

precipitation increases are modest. 
Great Lakes Climate Change Hydrologic Impact Assessment for 

IJC Lake Ontario—St. Lawrence River Study 

(Hydrology and Hydraulics Technical Working Group) 

US Analysis of Great Lakes Net Basin Supplies For Extreme Climate Scenarios 

This project estimates hydrological impacts of changed climates over the Great Lakes from the 

latest general circulation model results for the International Joint Commission’s five-year study of 

Lake Ontario—St. Lawrence regulation. This report concerns the US study of climate change 

performed by The Great Lakes Environmental Research Laboratory. 

Project Rationale 

Background 

The International Joint Commission (IJC) is conducting a Study for Criteria Review in the Orders 

of Approval for Regulation of Lake Ontario—St. Lawrence River Levels and Flows. In recent 

IJC and US Global Change Research Program studies, The Great Lakes Environmental Research 

Laboratory (GLERL) completed modeling of hydrologic impacts of climate change for the Great 

Lakes region. This work used climate change scenarios from two general circulation models 

(GCMs) and transformed them into hydrological impacts with models of rainfall/runoff, lake 

evaporation, connecting channel flows, lake regulation, and lake water balances. However, climate change scenarios were not included in this work for the Ottawa River basin and lower St. 

Lawrence River. In 2001, GLERL made GCM scenarios available over these extended areas and 

hydrologic modelers at Hydro Quebec extended, in 2002, the estimation of climate change hydrological impacts over these areas. GLERL and Hydro Quebec, under the auspices of the Hydrology and Hydraulics Technical Working Group (H&H TWG), coordinated their climate change 

methodologies in preparation for a new joint assessment of climate change impacts on hydrology 

over the entire Great Lakes—St. Lawrence River basin attendant to the latest GCM simulations 

(the Canadian and U.K. Hadley GCMs). Their cooperative examples concerned the future 20-

year periods for 2030 (2021-2040), 2050 (2041-2060), and 2090 (2081-2100), used by GLERL 

for the US National Assessment and IJC Reference on Consumption, Diversions and Removals of 

Great Lakes Water. They used the Canadian Centre for Climate Modelling and Analysis’s Coupled General Circulation Model version 1 (CGCM1) and the United Kingdom’s Hadley Centre 

Climate Model version 2 (HadCM2), both using IS92A emissions forcing scenarios. 

GLERL has since worked with the Ottawa hydrologic modeling group, consisting of researchers 

at Hydro Quebec and the Ministère de l’Environnement (Province of Quebec), on the future 30-

year period for 2050 (2040-2069), as determined of interest to the IJC study by the H&H TWG at 

their climate change workshop in 2002. In a contracted report prepared for the H&H TWG on 

the Canadian Climate Impacts Scenarios Project, prior to the 2002 workshop, Dr. Elaine Barrow 

selected GCM climate change scenarios for the Great Lakes-St. Lawrence region (Barrow 2002) 

according to the recommendations of the Intergovernmental Panel on Climate Change (IPCC) 

Task Group on Scenarios for Climate Impact Assessment (IPCC 2000). Output from nine GCMs 

and 34 climate change model run experiments was available for the construction of climate change 

scenarios. However, only five GCMS provided the climate variables required for hydrologic 

modeling (minimum and maximum air temperature, precipitation, wind speed, solar radiation, and 

humidity), but this still provided a set of 27 climate change scenarios over the study area. The 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 2

candidate GCMs included version 1 and 2 models from the Canadian Centre for Climate Modeling 

and Analysis (respectively, CGCM1 and CGCM2), the German Max Planck Institute for Meteorology’s model (ECHAM4), and version 2 and 3 models from the United Kingdom Hadley Centre 

for Climate Prediction and Research (respectively, HadCM2 and HadCM3). Scenarios were constructed from both recent (IS92A) and the newest (SRES) emission scenarios. The H&H TWG 

used scatter plots (of areally averaged annual changes in mean temperature and annual precipitation) to determine the choice of GCMs for scenario development in the hydrologic modeling. The 

goal was to “box the uncertainty” by selecting four scenarios of climate change that depict 1) 

most warming and wettest, 2) most warming and driest, 3) least warming and wettest, and 4) least 

warming and driest conditions over the IJC study region. While four GCM scenarios were chosen 

at the time of the workshop, newer GCM model runs using SRES forcing scenarios became available, subsequent to the workshop, and the H&H TWG wanted to use these latest experiments . 

Dr. Elaine Barrow again provided the H&H TWG with additional GCM climate change scenario 

output for six GCMs and 28 SRES model run experiments. H&H TWG personnel Joan Klaassen 

and Linda Mortsch and their subcontractor Marianne Alden repeated the determination of GCM 

scenarios. The GCM selection was again constrained to GCMs with climate variables required 

for hydrologic modeling. Four GCMs were selected, including the Canadian CGCM2, the German ECHAM4, the Japanese CCSR and the United Kingdom HadCM3. A new set of four GCM 

scenarios was selected from the resulting 24 climate change scenarios for use in the IJC study. 

They are: HadCM3 A1FI (warm and wet), HadCM3 B22 (not as warm but wet), CGCM2 A21 

(warm and dry), and CGCM2 B23 (not as warm but dry). Scenarios were not created from the 

GCM ensemble mean of runs (because of issues of consistency between the averaged climate elements), but only individual model runs were used. GLERL acquired the identified GCM climate 

change scenarios and made them available over the extended Great Lakes—St. Lawrence area to 

hydrologic modelers at Hydro Quebec and the Ministère de l’Environnement. 

As recommended by the H&H TWG climate change workshop and in consultation with Dr. Elaine 

Barrow, downscaling of the GCM scenarios is limited to interpolation of the GCM grids. Other, 

more labor intensive and detailed downscaling techniques such as statistical downscaling (i.e. 

SDSM) or weather generators (i.e. LARS-WG, as described in Dr. Barrow’s report prepared 

prior to the workshop) are not used. Downscaling of more than 1600 stations within the Great 

Lakes-St. Lawrence basin does not produce spatially coherent results or cost-effective, value 

added results. A regional climate model (RCM) scenario would be beneficial but neither Canadian nor US RCM results will be available in time to use for this study. 

Present Study 

GLERL extracted, and supplied to Hydro Quebec, GCM output changes between a baseline period of 1961—1990 and a future 30-year period (2040—2069). GLERL adjusted historical meteorology data for the Great Lakes basin with the GCM climate changes while Hydro Quebec and 

the Ministère de l’Environnement did the same for the Ottawa River basin. GLERL used a base

climate (observed data) time series over 1950—1999 to define the reference suggested by the 

IPCC of 1960—1990. GLERL simulated Great Lakes hydrology to estimate net water supply 

scenarios for each lake under each climate scenario. Hydro Quebec and the Ministère de 

l’Environnement did the same for the Ottawa River basin by using the appropriate hydrology and 

management models. Finally, GLERL, Hydro Quebec, and the Ministère de l’Environnement 

combined their estimates for the IJC study of Lake Ontario—St. Lawrence River regulation. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 3

Introduction 

Climatic change will impact on many aspects of the hydrological cycle with consequences for 

mankind that are interrelated and often difficult to discern. Climate warming will have impacts on 

Great Lakes water supply components, and basin storages of water and heat, that must be understood before lake level impacts can be assessed. Because the Laurentian Great Lakes possess 

tremendous water and heat storage capacities, they respond slowly to changed meteorological 

inputs. This memory damps short-term meteorological fluctuations, but allows response to 

longer-period fluctuations characteristic of climate change. Thus the large Great Lakes system is 

ideal for studying regional effects of climate changes. 

Early Great Lakes Climate Change Impact Studies 

Considerations of future climate situations that may occur (scenarios) help to identify possible effects and can bound future conditions, if widely different scenarios are tested. Preliminary impact 

estimates considered simple constant changes in air temperature or precipitation. Quinn and 

Croley (1983) estimated net basin supply to Lakes Superior and Erie. Cohen (1986) estimated 

net basin supply to all Great Lakes. Quinn (1988) estimated lower water levels due to decreases 

in net basin supplies on Lakes Michigan-Huron, St. Clair, and Erie. 

Beginning with Manabe and Wetherald (1975), researchers have run general circulation models 

(GCMs) of the earth's atmosphere to simulate climates for current conditions and for a doubling 

of global carbon dioxide levels (2xCO2). This 2xCO2 benchmark remained a widely used measure 

of greenhouse warming sensitivity through the early 1990s, when scenarios of transient increases 

in greenhouse gases using coupled atmosphere-ocean GCMs supplanted it. Using a global domain and coarse spatial resolution (evolving over time from roughly 8 degrees to 3 degrees), these 

models produce many internally consistent dialy meteorological values. The U.S. Environmental 

Protection Agency (USEPA 1984) and Rind (personal communication, 1988) used the hydrological components of general circulation models. They assessed changes in water availability in several regions throughout North America, but the regions were very large. Rind used only four regions for the entire continent and indicated needs for smaller region assessments. Regional hydrological models can link to GCM outputs to assess changes associated with climate change scenarios. Allsopp and Cohen (1986) used Goddard Institute of Space Sciences (GISS) 2xCO2 climate 

scenarios with net basin supply estimates. 

Other efforts that linked hydrological models to GCM outputs originated in studies commissioned 

by the U. S. Environmental Protection Agency (EPA). EPA, at the direction of the U.S. Congress, coordinated several regional studies of the potential effects of a 2xCO2 atmosphere. The 

studies addressed various aspects of society, including agriculture, forestry, and water resources 

(USEPA 1989). They directed others to consider alternate climate scenarios by changing historical meteorology similar to the changes observed in GCM simulations of 2xCO2, observing 

changed process model outputs, and comparing to model results from unchanged data. Cohen

(1990a, 1991) discusses other studies that use this type of linkage methodology and also presents 

his concerns for comparability between studies using different types. 

Recent Great Lakes Climate Change Impact Studies 

GLERL-EPA 2xCO2 Impacts. As part of the 1989 EPA study, the Great Lakes Environmental 

Research Laboratory (GLERL) assessed steady-state and transient changes in Great Lakes hy-
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 4

drology consequent with simulated 2xCO2 atmospheric scenarios from three GCMs (Croley 1990; 

Hartmann 1990; USEPA 1989). EPA required that GLERL first simulate 30 years of “present” 

Great Lakes hydrology by using historical daily data with present diversions and channel conditions. GLERL arbitrarily set initial conditions but used an initialization period to allow their models to converge to conditions initial to the simulation. GLERL repeated their simulation, with initial conditions set equal to the end conditions over the simulation period, until these conditions 

were unchanging. This facilitated investigation of “steady-state” conditions. The next step was to 

conduct simulations with adjusted data sets. 

EPA obtained output from atmospheric GCM simulations, representing both “present” and 2xCO2

steady-state conditions, from GISS, the Geophysical Fluid Dynamics Laboratory (GFDL), and the 

Oregon State University (OSU). They supplied monthly adjustments of “present” to 2xCO2 for 

each meteorological variable. GLERL applied them to daily historical data sets to estimate 33-

year sequences of atmospheric conditions associated with the 2xCO2 scenarios. This method 

keeps spatial and temporal (inter-annual, seasonal, and daily) variability the same in the adjusted 

data sets as in the historical base period. GLERL then used the 2xCO2 scenarios in hydrology 

impact model simulations similar to those for the base case scenario. They interpreted differences 

between the 2xCO2 scenario and the base case scenario as resulting from the changed climate. 

They observed that the three scenarios changed precipitation little but snowmelt and runoff were 

greatly decreased, evapotranspiration and lake evaporation were greatly increased, and net basin 

supplies to the lakes and lake levels were decreased. The scenario derived from the GFDL GCM 

was the most extreme with evaporation 44% higher than the base case and net basin supply less 

than 50% of the base case. 

Other EPA studies at that time include partial assessments of large-lake heat storage associated 

with climate change on Lakes Michigan (McCormick 1989) and Erie (Blumberg and DiToro

1989). The IJC study looked in less detail but more breadth at large-lake thermodynamics in that 

while only lake-wide effects were considered, all lakes were assessed. 

GLERL-IJC 2xCO2 Impacts. The 1989 EPA studies, in part, and the high water levels of the mid 

1980s prompted the International Joint Commission (IJC) to reassess climate change impacts on 

Great Lakes hydrology and lake thermal structure. GLERL adapted the 1989 EPA study methodology for the IJC studies (Croley 1992b) to consider 2xCO2 GCM scenarios supplied by the 

Canadian Climate Centre (CCC) for the period 1948-88. GLERL’s procedure to estimate 

"steady-state" suggested, for a few subbasins, very different initial groundwater storages than 

were used in model calibrations. Since there is little confidence in estimates of very large 

groundwater half-lives on these subbasins with only 10 to 20 years in calibrations, those initial 

values used in calibrations were also used in the simulations for those subbasins. 

Average monthly meteorological outputs were supplied for each month of the year over a 1o latitude by 1o longitude grid (Louie 1991) by the CCC as resulting from their second-generation 

GCM; see McFarlane (1991). GLERL computed 2xCO2 monthly adjustments at each location, 

used them with historical data to estimate the 2xCO2 41-year sequences (1948-88) for each Great 

Lake basin, and then used the 2xCO2 scenario in simulations similar to the base case as before. 

This scenario proved similar to the earlier GFDL-based scenario in that net basin supplies were 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 5

reduced to almost 50% of the base case. However, the CCC-based scenario reduced runoff more 

and evaporation less than the GFDL-based scenario. 

GCM Linkage Problems 

The hydrological study results from the 1989 EPA and IJC studies should be used with caution. 

They are, of course, dependent on GCM outputs with inherent large uncertainties in the GCM 

components, assumptions, and data. Transfer of information between the GCMs and GLERL's 

hydrological models in the manners described above involves several assumptions. Solar insolation at the top of and through the atmosphere on a clear day is assumed to be unchanged under 

the changed climate, modified only by changes in cloud cover, humidity, or (lately) aerosols. 

Over-water corrections are made in the same way, albeit with changed meteorology, which presumes that over-water/over-land atmospheric relationships are unchanged. 

Heat budget data from GCM simulations for Great Lakes grid points may not adequately describe 

conditions over the lakes due to the coarse resolution of the grids. GLERL's procedure for transferring information from the GCM grid is an objective approach but simple in concept. It ignores 

interdependencies in the various meteorological variables as all are averaged independently in the 

same manner. Of secondary importance, the spatial averaging of meteorological values over a 

box centered on the GCM grid point (implicit in the use of the nearest grid point to each square 

kilometer of interest) filters all variability that exist in the GCM output over that box. If GCM 

output were interpolated between these point values, then at least some of the spatial variability 

might be preserved. The interpolation performed by Louie (1991) from the original GCM grid to 

a finer grid reduced this problem, but it still exists in the use of the finer grid with the hydrology 

models. Of course, little is known about the validity of various spatial interpolation schemes and, 

for highly variable spatial data, they may be inappropriate. Furthermore, much of the variability at 

the smallest resolvable scale of GCMs is, unfortunately, spurious. 

Spatial and temporal variabilities in meteorology of the 2xCO2 data sets are the same as the base 

case, in both the 1989 EPA and IJC studies. The methodology does not address changes in variabilities that would take place under a changed climate. The method of coupling does not reproduce seasonal timing differences under a changed climate from the GCMs but preserves seasonal 

meteorological patterns as they exist in the historical (base case) data. This is a result of applying 

simple ratios or differences to calculate 2xCO2 scenarios from base case scenarios. This implicitly 

ignores spatial and temporal phase and frequency changes consequent in the 2xCO2 GCM simulations. For example, a changed climate alters the movement (direction, speed, frequencies) of air 

masses over the lakes. This implies an alteration of the seasonal temporal structure for storms and 

cyclonic events as well as the intensities of storms. The above method only allows modification of 

the latter. Seasonal changes induced by the changed meteorology because of a time-lag storage 

effect are observable, however. Shifts in snow pack or in the growth and decay of water surface 

temperatures are examples. Changes in annual variability are less clear, again as a result of using 

the same historical time structure for both the base case and the changed climate scenarios. 

Finally, the use of GCM outputs in the 1989 EPA and IJC studies, to drive GLERL’s hydrological 

process models, forced the use of inappropriately large spatial and temporal scales for studying 

the Great Lakes impacts of climate change. While the hydrological process models were defined 

over daily intervals and subbasin areas averaging 4,300 km2

, the GCM adjustments were made 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 6

over monthly time intervals and grids of 7.83° latitude by 10° longitude (GISS), 4.44° by 7.5° 

(GFDL), and 4° by 5° (OSU), and 3.75° by 3.75° interpolated to 1° by 1°(CCC GCM). 

Climate Transposition 

While the 1989 EPA and IJC studies looked at changes in the mean values of hydrological variables, changes in variability were unaddressed. This variability is the singular key problem for 

shipping, power production, and resource managers. GLERL and the Midwest Climate Center 

(MCC) recognized the importance of investigating the effects of shifts in the daily, seasonal, inter 

annual, and multi-year climate variability on lake net supply behavior, as well as related changes in 

mean supplies. They considered studies that used climate change scenarios that were not drawn 

so directly from historical data that they preserved historical spatial and temporal patterns. Such 

“instrumental analogues” are one empirical approach identified by Robinson and Finkelstein

(1989) to develop realistic scenarios since the actual values of the past were used to form the wet 

and dry extremes. However, the climate changes represented by these 12-year time series were 

not as large as many GCMs predict could happen in the future over the basin, and the effect of 

weather fluctuations over time due to large climatic changes could not be assessed by that approach. Atmospheric modelers are developing nested mesoscale numerical models of the Great 

Lakes basin (Bates et al. 1995) but these are not yet capable of generating multi-decadal series of 

conditions essential for the sensitivity study. In summary, these approaches simply could not provide the spatial and long temporal climatic data needed for the hydrological model and can not 

accomplish the desired sensitivity study of fluctuations in the hydrological system of the Great 

Lakes. 

GLERL and MCC investigated these changes in variability by utilizing data for climates which 

actually exist to the south and west of the Great Lakes and that resemble some of the 2xCO2

GCM scenarios. Lengthy (at least 40 years) and detailed records of daily weather conditions at 

about 2000 sites were available to represent physically plausible and coherent scenarios of alternate climates. Such data sets incorporated reasonable values and frequencies of extreme events, 

ensuring that the desired temporal and spatial variabilities were represented, and were being 

transposed over the Great Lakes. 

MCC supplied the data and GLERL transposed them to the Great Lakes by relocating all meteorological station data and Thiessen-weighting to obtain areal averages over the 121 watersheds 

and 7 lake surfaces for all days of record (1948-1992). GLERL also reduced all historical data 

(base case) within the Great Lakes (1900-1990). This involved extensive error checking and data 

correction for thousands of stations, and regeneration of areal averages. Since the Great Lakes 

affect the climate near the shoreline and these effects are not present in the transposed data sets, 

MCC prepared maps of generalized seasonal lake effects on the area's meteorology, to be applied 

to the transposed climates. 

The Great Lakes hydrology of each transposed climate was estimated, as before, by applying the 

system of hydrological models to these data sets (but this time, directly) and comparing outputs 

for each transposed climate to a base case derived with the model outputs from historical meteorological data. This approach allowed preservation of reasonable spatial and temporal variations 

in meteorology and preserves the interdependencies that exist between the various meteorological 

variables. It also allowed the use of appropriate spatial and temporal scales, better matching the 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 7

models than do the GCM output corrections. Similar studies were made to transpose the climate 

occurring during the 1993 Mississippi flood to assess climate change impacts on hydrology in the 

Great Lakes (Quinn et al. 1997). 

The transposed climates lead to higher and more variable over-land evapotranspiration and lower 

soil moisture and runoff with earlier runoff peaks since the snow pack is reduced up to 100%. 

Water temperatures increase and peak earlier. Heat resident in the deep lakes increases throughout the year. Buoyancy-driven water column turnover frequency drops and lake evaporation increases and spreads more throughout the annual cycle. The response of runoff to temperature 

and precipitation changes is coherent among the lakes and varies quasi-linearly over a wide range 

of temperature changes, some well beyond the range of current GCM predictions for doubled 

CO2 conditions. 

US National Assessment of Climate Change in the Great Lakes 

A more recent quantification of the effects of climate change on Great Lakes levels is documented 

in Lofgren et al. (2002). This study, funded by EPA, was a part of the US National Assessment 

of the Potential Consequences of Climate Variability and Change (NACC), which was part of the 

US Global Change Research Program. The study used as input the results of the version 1 Canadian model, CGCM1, and the version 2 United Kingdom model, HadCM2. Each of these is an 

earlier version of the two GCMs used in the present study, current in 1999, when the NACC 

study was initiated. The major improvement in these GCM runs over those used in prior studies 

is that the scenarios created a time series of simulated climate with a prescribed gradual increase 

in greenhouse gas concentrations. This enabled the investigation of climate change effects within 

any chosen range of years within the scenario, not just at a static level of greenhouse gases. The 

use of transient greenhouse gas concentrations was made more realistic through the use of full 

coupling between the atmospheric and oceanic components of these GCMs. Also new was the 

use of parameterizations of the direct radiative effect of sulfate aerosols, a mechanism that gained 

recognition during the 1990s as an effect with a significant trend, beginning with Charlson et al.

(1992). Finally, these models were run in an ensemble of realizations, each with slightly different 

initial conditions, but quickly evolving into independent time sequences of climate variables, but 

each remaining consistent with the same time series of forcing factors (i.e. greenhouse gas and 

aerosol concentrations). 

Lofgren et al. (2002) found that CGCM1 predicted increased temperature and precipitation into 

the future. However, the increased evaporation associated with increased temperature overbalanced the increased precipitation, and resulted in lake levels lowered by up to 0.72 m in a time 

period centered about 2030 relative to a base time period centered at 1989, and a drop of as much 

as 1.38 m for a time period centered at 2090. The HadCM2 model also had increases in both 

temperature and precipitation. However, the increase in temperature was much less than in 

CGCM1 and the increase in precipitation was much greater and tended to take the more dominant 

role. For the 2030 time period, the changes in lake levels ranged among the Great Lakes from a 

drop of 0.01 m to a rise of 0.05 m. For the 2090 time period, rises in lake levels ranged from 0.01 

m to 0.35 m. 

Lofgren et al. (2002) also showed decreases in lake ice cover, with larger decreases in the 

CGCM1 runs than in the HadCM2 runs. They simulated effects of greenhouse warming on the 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 8

supply of groundwater for municipal use in the vicinity of Lansing, Michigan, illustrating the possibility of complete drawdown of the aquifer in some spots [see also Croley and Luukkonen

(2003)]. They also used an interest satisfaction model, which attempted to quantify the degree to 

which shipping and hydropower interests in the upper St. Lawrence River and the outlet of Lake 

Ontario might be satisfied, given the projected changes in lake levels and water supplies. This 

model showed considerably reduced interest satisfaction for most of the interests when using the 

output from the CGCM1, but little change when using the HadCM2. 

Present Study 

GLERL extracted GCM output changes between a baseline period of 1961—1990 and the future 

30-year period 2040—2069 for models: HadCM3 A1FI (warm/wet), HadCM3 B22 (not as 

warm/wet), CGCM2 A21 (warm/dry), and CGCM2 B23 (not as warm/dry). They provided these 

changes for: daily precipitation increase (ratio), minimum daily air temperature increase at 2 m 

(°C), average daily air temperature increase at 2 m (°C), maximum daily air temperature increase 

at 2 m (°C), wind speed increase at 2 m (ratio), specific humidity increase (ratio), and cloud cover 

increase (ratio). GLERL adjusted historical daily meteorology data for the Great Lakes basin 

over 1950—1999 with the GCM climate changes and simulated Great Lakes hydrology under the 

various scenarios. GLERL used their conceptual models for simulating moisture storages in, and 

runoff from, the 121 watersheds draining into the Laurentian Great Lakes, over-lake precipitation 

into each lake, and the heat storages in, and evaporation from, each lake. GLERL combined these 

components as net water supplies for each lake to consider the climate scenarios. 

This 2003 GLERL study of climate scenarios in the Great Lakes basin for the IJC Lake Ontario—

St. Lawrence River study is presented here. The next section (Great Lakes Dynamics and Climate) describes the present Great Lakes climate, the physical characteristics of the Great Lakes 

and the dynamics of these large water bodies. The following section (Methodology) outlines the 

methodology of climate scenario consideration from GCM experiments. The hydrological models 

for basin runoff, over-lake precipitation, and lake thermodynamics are described in the next section (Great Lakes Physical Process Models) and results from these models are presented in the 

succeeding section (Great Lakes Climate Change Hydrologic Response). The final section (Hydrological Sensitivities) recapitulates the major points of this research. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 9

Great Lakes Dynamics and Climate 

There is a major tendency to think of Great Lakes water levels in terms of extremes rather than of 

normal conditions. Within recent memory we had the record low lake levels of 1964. This resulted in docks sitting out of the water, insufficient depths for navigation in many harbors and 

channels, and greatly reduced recreational opportunities. Record high lake levels with resultant 

flooding and shore damage and erosion followed these low levels in 1973. The lake levels remained high until 1986 and new record highs were once again set on Lakes Superior, MichiganHuron, St. Clair, and Erie, after which they returned to near-average conditions,. More recently 

(2000-2003) we again experienced low level conditions on all lakes. 

This section presents an overview of the physical characteristics of the Great Lakes from a water 

quantity perspective, outlines the basin and lake physical processes, summarizes the climatology 

of the Great Lakes, examines the types of natural lake level fluctuations and their causes, compares the natural fluctuations with existing diversions and regulation effects, describes current 

conditions, and concludes with a long-term perspective on lake levels. 

Great Lakes Overview 

The Great Lakes basin, in 

Figure 1, has an area of approximately 770,000 km2

(300,000 mi2

), about onethird of which is water surface. Others give cursory 

descriptions; see Freeman 

and Haras (1978), the U. 

S. Army Corps of Engineers (1985), and the Coordinating Committee on 

Great Lakes Basic Hydraulic and Hydrologic Data

(1977). The basin extends 

some 3,200 km (2,000 mi) 

from the western edge of 

Lake Superior to the 

Moses-Saunders Power 

Dam on the St. Lawrence 

River. The water surface 

drops in a cascade over this 

distance some 180 m (600 

ft). The most upstream, largest, and deepest lake is Lake Superior. The lake has two interbasin 

diversions of water into the system from the Hudson Bay Basin: the Long Lac and Ogoki Diversions. Lake Superior waters flow through the lock and compensating works at Sault St. Marie 

and down the St. Mary’s River into Lake Huron where it is joined by water flowing from Lake 

Michigan. Lake Superior is completely regulated, to balance Lakes Superior, Michigan, and 

Kilometers

0 100 200

N

St. Clair

Michigan

Superior

Erie

Huron

Ontario

Gr eat Lakes Drainage Basin Limit

Great Lake s Dr ainag e Basin Limit

Georgian Bay

43oN 43oN

84 Wo

84 Wo

Figure 1. The Laurentian Great Lakes Basin. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 10

Huron water levels, according to Regulation Plan 1977, under the auspices of the International 

Joint Commission (International Lake Superior Board of Control 1981, 1982). 

Lakes Michigan and Huron are considered to be one lake hydraulically because of their connection through the deep Straits of Mackinac. Another interbasin diversion takes place from Lake 

Michigan at Chicago. Here water is diverted from the Great Lakes to the Mississippi River Basin. 

The water flows from Lake Huron through the St. Clair River, Lake St. Clair, and Detroit River 

system into Lake Erie. The drop in water surface between Lakes Michigan-Huron and Lake Erie 

is only about 2 m (8 ft). This results in a large backwater effect between Lakes Erie, St. Clair, 

and Michigan-Huron; changes in Lakes St. Clair and Erie levels are transmitted upstream to Lakes 

Michigan and Huron. From Lake Erie, the flow is through the Niagara River and Welland Diversion into Lake Ontario. The major drop over Niagara Falls precludes changes on Lake Ontario 

from being transmitted to the upstream lakes. The Welland Diversion is an intrabasin diversion 

bypassing Niagara Falls and is used for navigation and hydropower. There is also a small diversion into the New York State Barge Canal System, which is ultimately discharged into Lake Ontario. Lake Ontario is completely regulated in accordance with Regulation Plan 1958D to balance 

interests upstream on Lake Ontario with those downstream on the St. Lawrence Seaway [estimated to have lowered Lake Ontario 0.75 m (2.5 ft) during the record high water levels of 1986]. 

The Moses-Saunders Power Dam between Massena, New York and Cornwall, Ontario controls 

the outflows. From Lake Ontario, the water flows through the St. Lawrence River to the Gulf of 

St. Lawrence and to the ocean. 

Lakes Superior, Michigan, Huron, and Ontario are very deep, while Lakes Erie and St. Clair are 

very shallow. Table 1 contains pertinent gross statistics on the sizes of the Great Lakes, Lake St. 

Clair, and their basins. 

Physical Processes 

The behavior of the Laurentian Great Lakes system is governed by its huge storages of water and 

energy. There are three main conservation laws to consider relative to these huge storages: 1) 

mass balances in the basins, 2) mass balances in the lakes, and 3) energy balances in the lakes. 

There are also mass and energy balances to consider for the lakes' ice cover. The first conservaTable 1. Laurentian Great Lake Size Statisticsa

. 

Characteristic Superior Michigan Huron St. Clair Erie Ontario

Basin Areab, km2 128,000 118,000 131,000 12,400 58,800 60,600

 mi2 49,300 45,600 50,700 4,800 22,700 23,400

Surface Area, km2 82,100 57,800 59,600 1,114 25,700 18,960

 mi2 31,700 22,316 23,000 430 9,920 7,320

Volume, km3 12,100 4,920 3,540 3 484 1,640

 mi3 2,900 1,180 850 1 116 393

Average Depth, m 147 85 59 3 19 86

 ft 482 280 190 10 62 280

Maximum m 405 281 229 6 64 244

ft 1,330 923 750 21 210 802 a

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data (1977). 

b

This does not include the surface area of the lake. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 11

tion law (mass balance on the basins) 

comprises the primary process determining lake levels: the hydrological cycle of 

the Great Lakes Basin (Croley 1983a). 

As shown in Figure 2, precipitation enters the snow pack, if present, and is 

then available as snow melt depending 

mainly on air temperature and solar radiation. Snowmelt and rainfall partly 

infiltrate into the soil and partly run off 

directly to rivers, depending upon the 

moisture content of the soil. Infiltration 

is high if the soil is dry, and surface runoff is high if the soil is saturated. Soil 

moisture evaporates or is transpired by 

vegetation depending upon the types of 

vegetation, the season, solar radiation, 

air temperature, humidity, and wind 

speed. The remainder percolates into 

deeper basin storages, which feed the 

rivers and lakes through interflows and 

groundwater flows. Generally, these 

river supplies are high if the soil and 

groundwater storages are large. Because of this buffering effect of the large snow pack and the large soil, groundwater, and surface 

storages, runoff from rivers into a lake can remain high for many months or years after high precipitation has stopped. 

Mass conservation in the lake is the next major determinant of lake levels. Major sources of water into a lake include precipitation on the land basin, which results in runoff into the lake, precipitation over the lake surface, inflow from upstream lakes, and diversions into the lake. Net 

groundwater flows directly to each of the Great Lakes are generally neglected (DeCooke and 

Witherspoon 1981). The outflows consist of evaporation from the lake surface, flow to downstream lakes, and diversions. The imbalance between the inflow and outflow results in the lake 

levels either rising if there is more inflow than outflow, represented by a positive change in storage, or falling if there is more outflow than inflow, represented by a negative change in storage. 

The large lake water storages provide a buffering of the input fluctuations with regard to output 

variations. The large surface areas of the lakes enable large storage changes with very small water 

level changes; hence, outputs (which are a function of water levels) change slowly. 

Energy conservation in a lake actually must be considered together with a lake's mass balance. 

Lake heat storage is a function of the lake's size and shape and of its surface inputs of solar insolation and reflection (short wave exchanges), thermal emission and atmospheric emission (net long 

wave exchange), conduction to the atmosphere (sensible heat transfer), heat loss through evaporation (latent and some advection), other advection terms (precipitation, inflows, and outflows), 

and ice growth and melt. Evaporation is a function of surface temperature (heat storage), air 

UPPER SOIL 

ZONE MOISTURE

LOWER SOIL 

ZONE MOISTURE

GROUNDWATER 

ZONE MOISTURE

SURFACE 

STORAGE

SNOW 

PACK

INSOLATION 

PRECIPITATION 

TEMPERATURE

SNOW RAIN

MELT RUNOFF

EVAPOTRANSPIRATION

EVAPOTRANSPIRATION

EVAPOTRANSPIRATION

SURFACE

RUNOFF

INTERFLOW

GROUND

WATER

PERCOLATION

DEEP 

PERCOLATION

BASIN OUTFLOW

EVAPORATION

Figure 2. Great Lakes Subbasin Mass Balance 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 12

temperature (atmospheric stability), humidity, and wind speed. Water surface temperatures generally peak in August (September for Superior) at 15-25°C resulting in stable summertime temperature stratification in the water column (high-density cool water at depth and low-density 

warm water at the surface). Surface temperatures drop during the fall and winter, and the water 

column in each lake "turns over" as temperatures drop through 4°C where water density is maximum (now-heavier surface layers sink and mix with deep now-lighter waters). Turn over occurs 

again in the spring as surface temperatures rise to that of maximum density. 

There is also extensive ice cover on most of the lakes during most winters. Lake Superior averages about 75% ice-covered, Michigan is 45%, Huron is 68%, Erie is 90%, and Ontario is 24%. 

Ice formation and breakup is governed by additional mass and energy balances that take place simultaneously with those of the lakes' water bodies. The Great Lakes do not ordinarily freezeover completely (Assel et al. 1983) because of the combination of their large heat storage capacity, large surface area, and their location in the mid-latitude winter storm track. Alternating periods of mild and cold air temperatures combine with episodic high and low wind stresses at the 

water surface to produce transitory ice conditions during the winter. Ice cover in mid-lake regions is often in motion. Lake Erie ice speeds have been observed to average 8 cm/s with a 

maximum speed of 46 cm/s (Campbell et al. 1987). Ice can form, melt, or be advected toward or 

from most mid-lake areas throughout the winter (Rondy 1976). When ice is advected into areas 

with existing ice cover, it can under- or over-ride the ice cover, forming rafted rubble 5-10 m 

thick. The normal seasonal progression of ice formation begins in the shallow shore areas of the 

Great Lakes in December and January. The deeper mid-lake areas normally do not form extensive ice cover until February and March. Ice is lost over all lake areas during the last half of 

March and during April. 

Ice formation alters the surface thermodynamics of the lakes, changing subsequent ice formation, 

surface heating or cooling, lake evaporation, and lake responses to atmospheric changes. The 

large heat storages of the lakes provide a buffering; they forestall and reduce ice formation and 

shift the large evaporation response. Water temperatures lag air temperatures and evaporation 

lags surface heating (insolation). Evaporation peaks in October-November on Lake Erie and in 

November-December on Lake Superior. 

The large basin and lake storages of water and ice and the large lake and ice storages of energy 

represent an “intrinsic memory” that allow scientists to forecast basin moisture storage and runoff 

(basin storage buffering) in the face of uncertain meteorology. It also allows prediction of evaporation (heat storage buffering) and lake levels (lake storage buffering) of up to about six months 

of low-frequency changes. It further enables estimation of ice formation amounts and timing as 

well as all secondary hydrological variables. 

Climatology 

Precipitation causes the major long-term variations in lake levels (Quinn and Croley 1981; Quinn

1985). Table 2 shows that annual precipitation ranges from about 82 cm (32 in) for Superior to 

93 cm (37 in) for Ontario. Figure 3 depicts total annual precipitation over Lakes MichiganHuron, St. Clair, and Erie for the 1900-1979 period (Quinn 1981; Quinn and Norton 1982). 

From 1900 through 1939, a low precipitation regime predominated with the majority of the years 

falling below the mean. From about 1940 until recently, a high precipitation regime has existed. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 13

Of particular interest is the high precipitation in the early 1950s, the low 

precipitation in the early 1960s that 

led to the record lows, and a consistently very high precipitation regime 

from the late 1960s through the late 

1980s. Table 3 summarizes Great 

Lakes annual precipitation totals by 

basin for several periods. Of particular interest are the progressions of 

increasing precipitation for each basin. While the 1940-90 period is 

generally above normal (2-8% higher 

than the 1900-69 average and -2-6% 

higher than the 1900-90 average), 

the last 20 of those years are higher still (8-13% than the 1900-69 average and 2-11% higher than 

the 1900-90 average); 1985 set many new records with the highest precipitation to that date (8-

40% higher than the 1900-69 average and 7-33% higher than the 1900-90 average). 

Variations in air temperature also influence lake level fluctuations. At higher air temperatures, 

plants tend to use more water, resulting in more transpiration, and there are higher rates of evaporation from both the ground surface and the lake. This yields less runoff for the same amount of 

precipitation than would exist during a low temperature period when there is less evaporation and 

transpiration. Coupled with the higher lake evaporation, lake levels drop with increasing air temperature, all other things being equal. The annual mean air temperature around the perimeter of 

the Great Lakes since 1900, summarized in Figure 4, indicate three distinct temperature regimes: 

a low temperature regime from 1900-1929, a higher temperature regime from about 1930-1959, 

Table 2. Partial Great Lakes Annual Water Balance (1951-1988). 

Component Superior Michigan Huron Erie Ontario 

 (cm) (in) (cm) (in) (cm) (in) (cm) (in) (cm) (in) 

Lake Precipitationa 82 32 83 32 87 34 81 36 93 37 

Lake Runoffa 62 24 64 25 84 33 80 32 169 67 

Lake Evaporationa

 56 22 65 25 63 25 90 35 67 26 a

Equivalent depth over the lake area.

Figure 3. Lakes Michigan, Huron, St. Clair, and Erie 3-

year-Mean Precipitation (1900-90) 

Table 3. Great Lakes Annual Precipitation Summary. 

Period Superior Michigan Huron Erie Ontario 

 (cm) (in) (cm) (in) (cm) (in) (cm) (in) (cm) (in) 

1900-39 72 29 78 31 77 31 85 34 86 34 

1940-90 81 32 82 33 86 34 89 35 93 37 

1970-90 84 33 86 34 89 35 94 37 98 39 

1985 98a

 39a 102a 40a 105a 41a 106 42 100 40 

1900-69b

 75 30 79 31 80 32 87 34 87 34 

1900-90b

 79 31 84 33 84 33 89 35 88 35 a

Record high for 1900-90. 

b

Long-term period averages are supplied for comparison.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 14

and an additional low regime from 1960-

present period. The difference between 

the previous and current regime is a drop 

of about 1°F. 

The magnitude of the hydrological variables varies with season, as shown in Figure 5 for Lake Erie (Quinn 1982; Quinn 

and Kelley 1983). The monthly precipitation is fairly uniformly distributed 

throughout the year, while the runoff has 

a peak during the spring which results 

primarily from the spring snow melt. The 

runoff is at a minimum in the late summer 

and early fall due to large evapotranspiration from the land basin. The lake evaporation reaches a minimum during the 

spring and gradually increases until it 

reaches a maximum in the late fall or early winter. The high evaporation period is due to very 

cold dry air passing over warm lake surfaces. The integration of these components is depicted in 

the net basin supply, which consists of the precipitation plus the runoff minus the evaporation. As 

seen from Table 2, these three components of net basin supply are all of the same order of magnitude for each lake. Annual runoff to the lake ranges from about 62 cm (24 in) for Superior to 169 

cm (67 in) for Ontario, and annual lake evaporation ranges from about 56 cm (22 in) for Superior 

to 90 cm (35 in) for Erie. The net basin supply is seen in Figure 5 to reach a maximum in April 

and a minimum in the late fall. The negative values indicate that more water is leaving the lake 

through evaporation than is being provided by precipitation and runoff. 

Lake Level Fluctuation and Trends 

There are three primary types of lake level fluctuations: long-term lake levels (represented on an annual 

basis), seasonal lake levels, and short-period lake 

level changes due to wind setup and storm surge. 

Annual fluctuations result in most of the variability 

leading to the record high and low lake levels. The 

annual lake levels are shown in Figure 6 from 1860 

through the present to illustrate the long-term variability of the system. The record highs in 1952, 

1973, and 1986 and record lows in 1935 and 1964 

are readily apparent. There is an overall range of 

about 2 m (6 ft) in the annual levels. Of particular 

interest is the fall in the levels of Lakes Michigan and 

Huron occurring in the mid-1880's from which the 

lakes never recovered. This probably results from 

dredging for deeper draft navigation in the St. Clair 

River. Other changes in the St. Clair River include 

Figure 4. Great Lakes Annual Air Temperature 

(1900-29, 1930-59, 1960-90) 

Figure 5. Lake Erie Seasonal Net Basin 

Supplies
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 15

sand and gravel dredging between 

about 1908 and 1924, a 7.6 m (25 ft) 

navigational project in the mid-1930's, 

and an 8.2 m (27 ft) navigation project in the late 1950's and early 1960's. 

Without these changes, Lake Michigan-Huron would be approximately 

0.5 m (1.5 ft) higher than it is today. 

The three-year precipitation mean in 

Figure 3 correlates very well with annual lake levels as observed by superimposing the annual precipitation on 

the annual Lake Erie water levels in 

Figure 7. The precipitation tends to 

lead the water levels by approximately 

one year, as shown here by the 1929 

highs, the 1935 lows, the 1952 highs, and the 1963 lows. In particular, the last 15 years of high 

precipitation resulted in very high water levels. Thus, the continuing high levels are the result of 

the increased precipitation regime since 1940 coupled with the lower temperature regime since 

1960. 

Superimposed on the annual levels are the seasonal cycles shown in Figure 8; each lake undergoes 

a seasonal cycle every year. The magnitude depends upon the individual water supplies. The 

range varies from about 30 cm (1 ft) on the upper lakes to about 38 cm (1.3 ft) on the lower 

lakes. In general, the seasonal cycles have a minimum in the winter, usually January or February. 

The levels then rise due to increasing water supplies from snow melt and spring precipitation until 

they reach a maximum in June for the smaller lakes, Erie and Ontario, and September in the case 

of Lake Superior. When the net water supplies diminish in the summer and fall, the lakes begin 

their seasonal decline. 

The final type of fluctuation, common 

along the shallower areas of the Great 

Lakes, particularly Lake Erie, Saginaw 

Bay, and in some cases on Green Bay, 

are storm surges and wind set-up. 

When the wind is blowing along the 

long axis of a shallow lake or bay, a 

rapid difference in levels can build over 

the water. This difference can be as 

large as 5 m (16 ft) for Lake Erie 

(storm of 2 December 1985). These 

storm conditions, when superimposed 

on high lake levels, cause most of the 

Great Lakes shoreline damage. 

Figure 6. Great Lakes Annual Water Levels (1900-90). 

Figure 7. Lake Erie Annual Water Levels and Precipitation
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 16

Looking in more detail at past trends 

in lake levels, along with more recent 

conditions for Lake Erie, we see a 

steady progression of changes in lake 

levels with time in Figure 9. These 

changes reflect the changes in precipitation, illustrated in Figure 3 and summarized in Table 3. At the bottom of 

Figure 9 are the record low lake levels 

for each month, which were set primarily in 1964. Proceeding upwards 

we have the 40-year average from 

1900-1939. From 1940-1979, the lake 

is at a still higher average level. Taking the 21-year period from 1970-

1990, we see that the lake level average is higher yet, followed by the record highs set in 1985. Record levels for the month were set 

in April and May 1985 on Lakes Michigan-Huron, St. Clair, and Erie; they were set for November 

1985 through April 1986 on Lakes Erie and St. Clair. Since that time, a record drought brought 

water levels back to their long-term normal values in the late 1980s and early 1990s. 

Diversions 

It is interesting to compare each impact of an existing diversion on all lakes levels in Table 4 with 

natural lake-level fluctuations (International Great Lakes Diversions and Consumptive Uses 

Study Board 1985). This enables a comparison of man's impacts with natural fluctuations. The 

Long Lac and Ogoki Diversions average about 160 m3

s

-1 (5,600 ft3

s

-1) and raise lake levels between 6 cm (0.21 ft) and 11 cm (0.37 ft). The Chicago Diversion averages about 90 m3

s

-1 (3,200 

ft3

s

-1) and lowers lake levels between 2 cm (0.07 ft) and 6 cm (0.21 ft). The Welland Canal, 

which bypasses Niagara Falls, averages about 270 m3

s

-1 (9,400 ft3

s

-1) and lowers lake levels between 2 cm (0.06 ft) and 13 cm (0.44 ft) with no effect on Lake Ontario. The combined effect on 

the lakes ranges from a 2 cm (0.07 

ft) rise for Lake Superior to a 10 

cm (0.33 ft) drop for Lake Erie. 

The diversion effects are therefore 

small in comparison with the one or 

more meter (several foot) variation 

associated with short-term storm 

movements, the 30-38 cm (1-1.3 ft) 

seasonal cycle, and the 2 m (6 ft) 

range of annual variations. 

The small effects of the diversions 

along with the long response time 

of the system illustrate why diversions are not suitable for lake regulation. Due to the large size of the 

Figure 8. Average Seasonal Great Lakes Levels (1900-90)

Figure 9. Lake Erie Seasonal Water Level Comparisons 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 17

Great Lakes system, it responds very slowly to man-induced changes. This is illustrated in Figure 

10 by the length of time it takes from the start of a hypothetical diversion on Lakes Michigan and 

Huron (of the magnitude of the Chicago diversion) until the ultimate effect of that diversion is 

reached on Lakes Michigan-Huron, and Erie. It takes approximately 3-3.5 years to achieve 50% 

of the ultimate effect and 12-15 years to get 99% of the effect. (These results depend somewhat 

on the lake levels at the beginning of the diversion.) Thus, regulation by diversion would not produce changes responsive to natural fluctuations. Recent studies at GLERL indicate that an increase of 10% in the Niagara River discharge from Lake Erie (and consequent increases in Lake 

Erie inflow) would lower it 27 cm (0.89 ft) in about 11-12 years and lower Lakes Michigan and 

Huron 14 cm (0.46 ft) in this same period. If Lake Erie inflows were held constant (not possible 

at the present time), then it would take 6 months to 1 year to achieve this lowering. 

Additional interbasin diversions are a highly controversial issue at the present time around the 

Great Lakes. Possible uses of Great Lakes water outside the basin are flow augmentation for 

navigation, energy uses such as synthetic fuels or pipelines, agriculture and aquifer recharge, and 

municipal water supplies. A small pipeline project such as the Powder River coal slurry pipeline 

would require 0.2 m3

s

-1 (7 ft3

s

-1) of water and would have no measurable impact on lake levels. A 

synthetic fuels project, highly unlikely at this time, could require approximately 23 m3

s

-1 (800 ft3

s

-

1

) and result in a lake level lowering of 1-2 cm (0.04-0.06 ft). A major agricultural or aquifer recharge project could require 300 m3

s

-1 (10,000 ft3

s

-1) and would result in lake level decreases 

ranging from 12 cm (0.4 ft) on 

Lake Erie to 21 cm (0.7 ft) on Lake 

Michigan-Huron. It should be emphasized that these are hypothetical 

projections for illustration only. 

Future 

Water levels ordinarily do not 

change quickly, as shown by the 

above consideration of diversions. 

Other studies at GLERL indicate 

that if normal meteorological conditions were realized (“normal” being 

the average conditions over 1900-

69) instead of the record drought of 

the late 1980s, it would have taken 

about 6 years for Lake MichiganHuron to return from its January 

Table 4. Impact of Existing Diversions on Lake Levels. 

Diversion Amount Superior Mich-Hur Erie Ontario 

 (m3s

-1) (ft3

s

-1) (cm) (ft) (cm) (ft) (cm) (ft) (cm) (ft) 

Ogoki-Long Lac 160 5600 +6 +0.21 +11 +0.37 +8 +0.25 +7 +0.22

Chicago 90 3200 -2 -0.07 -6 -0.21 -4 -0.14 -3 -0.10

Welland 270 9400 -2 -0.06 -5 -0.18 -13 -0.44 0 0 

COMBINED +2 +0.07 -1 -0.02 -10 -0.33 +2 +2 

Figure 10. Selected Great Lake Responses to Diversions 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 18

1986 level to its normal (1900-69) level. About 7 years would have been required for Lakes St. 

Clair and Erie to return to within 10 cm (4 in) of normal, and about 9 years would have been required for them to return to within 5 cm (2 in) of normal. Even supposing that we encountered a 

drought similar to the 1960-64 conditions, about 3.5 years would have been required for Lake 

Michigan-Huron and about 4 years would have been required for Lakes St. Clair and Erie. 

A long-term perspective on Lake Michigan levels for 7,000 years was reconstructed through geologic and archaeological evidence (Larsen 1985) under work sponsored by the Illinois State Geological Survey. Conditions several thousand years ago were not necessarily the same as today due 

to isostatic rebound and uplift during the intervening time. But, in general, this provides additional perspective on possible conditions we may experience in the future. Looking at just the last 

2,500 years, during which time the Great Lakes were in their current state, there were major lake 

level fluctuations. During most of this time the levels were much higher and more variable than 

they have been during the last 120 years of record. If the past is any indication, lake levels in the 

future could go through a considerably larger range than we have experienced lately. Indeed, the 

period of record, which makes up what many consider to be normal, the early 1900's through the 

1960's, may represent abnormal conditions. 

Summary Comments on Great Lakes Dynamics 

Huge storages of water in the basins and the lakes and of energy in the lakes give the Laurentian 

Great Lakes their characteristic behavior. They filter the variability of the meteorological inputs 

and enable hydrological predictions in the face of uncertain meteorology, if the storage amounts 

are known. Historically, lake levels are most affected by temporal patterns of precipitation; air 

temperature patterns play a lesser but important role also. It is important to keep in perspective 

that while we have ranges in annual lake levels of 1-2 m (4-6 ft), and additional short-term effects 

on the order of 2-3 m (7-8 ft), the effects of man on the system are relatively small, on the order 

of about 5 cm (0.2 ft). While the lakes are slow changing over the long term in the face of normal 

meteorology, past fluctuations have been very large. Future changes will depend mostly on future 

climate. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 19

Methodology 

Climate Data 

The Great Lakes hydrological 

models used in this study (described subsequently) require 

daily values of precipitation, air 

temperature, wind speed, humidity, and cloud cover or insolation 

at many surface locations. In 

past determinations of water 

supply effects from climate 

change scenarios (Croley 1990, 

1992b, 1993a; Croley and 

Hartmann 1989; Hartmann

1990; Lofgren et al. 2002), 

GLERL used about 1,800 meteorological stations for overland 

precipitation and air temperature 

and about 40 meteorological stations for over-lake air temperature, humidity, wind speed, and 

cloud cover (for determining insolation). Recent experience (Croley and Hartmann 1986, 1987) 

suggests that 200-300 stations per lake basin for overland meteorology and about 5-8 stations per 

lake for over-lake meteorology would be sufficient for operation of the large-area runoff and 

evaporation models at daily time intervals for studies of the type considered here. 

Daily maximum and minimum air temperatures, precipitation, and snowfall were obtained for the 

52-year period of 1948-1999 from the dense array of stations in the National Weather Service's 

cooperative observer network 

and from Environment Canada; 

see Figure 11. Out of this dense 

array of stations, a subset have 

daily records of wind speed, humidity, and cloud cover, and are 

generally located at the weather 

service offices and airport observing stations; see Figure 12. 

These stations were used in earlier studies (Croley 1990, 1992b, 

1993a; Croley and Hartmann

1986, 1987, 1989; Hartmann

1990; Lofgren et al. 2002); they 

were augmented here to extend 

their data period through 1999. 

The data reductions of these earlier studies, to determine areal 

Thiessen-averaged meteorologiFigure 11. Base Case Temperature and Precipitation Stations

Figure 12. Base Case Temperature, Humidity, Wind Speed, 

and Cloud Cover Stations 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 20

cal time series over each of the 121 sub-basins and the 7 lake surfaces, were enormous (Croley 

and Hartmann 1985), but the software for this was developed at that time. Now, improved computers allow re-reduction of all data in a timely fashion with this software. 

Changed Climate 

GLERL constructed a master computer procedure to integrate their Large Basin Runoff Model, 

over-lake precipitation estimates, and their lake evaporation models for all Great Lakes to provide 

a net water supply model for the entire Great Lakes system. They developed it specifically to 

look at the impact of changed climate by doing simulations with changed meteorology that represent scenarios of changed climate and comparing with simulations based on historical meteorology (representing an unchanged climate). Inputs are areal-average daily precipitation and maximum and minimum air temperatures for each of the 121 watersheds about the Great Lakes and 

areal-average daily air temperature, cloud cover, humidity, and wind speed for each of the five 

Great Lakes and Lake St. Clair. 

GLERL's general procedure for the investigation of steady-state behavior under a changed climate 

is similar to that used for the 1989 EPA study, as detailed elsewhere (Croley 1990; Louie 1991); 

it required that GLERL first simulate 50 years of “present” hydrology by using historical daily 

maximum and minimum air temperatures, precipitation, wind speed, humidity, and cloud cover 

data for the 1950-1999 period; this is called the “base case” scenario. The initial conditions were 

arbitrarily set but an initialization simulation period of 1 January 1948 through 31 December 1949 

was used to allow the models to converge to conditions (basin moisture storages, water surface 

temperatures, and lake heat storages) initial to the 1 January 1950 through 31 December 1999 

period. GLERL then attempted to estimate “steady-state” conditions, but there were problems. 

The procedure to estimate “steady-state” conditions is to repeat the 52-yr simulation with initial 

conditions (basin moisture storages, lake heat storages, and surface temperatures) set equal to 

their values at the end of the simulation period, until they are unchanging. This procedure requires much iteration for a few subbasins with very slow groundwater storages and suggests very 

different initial groundwater storages than were used in calibrations. Actually, the original calibrations of the models used arbitrary (but fixed) initial conditions. GLERL should have determined initial conditions also in the calibrations, but that was unfeasible; there is little confidence in 

calibrated parameter sets that suggest very slow groundwater storages (half-lives on the order of 

several hundred years in some cases) since only 10 to 20 years were used in the calibrations. 

Therefore, the best estimate of “present” hydrology is to use calibrated parameters with initial 

conditions on “the same order” as those assumed for the calibrations. GLERL did the latter and 

then conducted simulations with adjusted data sets. 

GLERL acquired average monthly differences (between base case and each climate change scenario) for air temperature (daily minimum, maximum, and average), relative humidities or vapor 

pressure, and solar radiation (from which they back-calculated cloud cover), and average monthly 

ratios for precipitation and wind speed for each month of the year. They did this for each of the 

GCM-generated climate change scenarios: HadCM3 A1FI (warm and wet, referred to henceforth 

as HADCM3A), HadCM3 B22 (not as warm but wet, referred to herein as HADCM3B), 

CGCM2 A21 (warm and dry, referred to as CGCM2A), and CGCM2 B23 (not as warm but dry, 

referred to as CGCM2B). GLERL inspected each of the 770,000 square kilometers within the 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 21

Great Lakes Basin to see which grid point it is closest to and applied the monthly adjustment at 

that grid point to data representing that square kilometer. By combining all square kilometers 

representing a watershed or a lake surface, GLERL derived an areally averaged adjustment to apply to their areally averaged historical data sets for the watershed or lake surface, respectively. 

They then used this climate change scenario in simulations similar to the base case scenario. They 

repeated the 52-yr simulation with initial conditions set equal to their values at the end of the 

simulation period, until they were unchanging to estimate “steady-state” future conditions. They 

then interpreted differences between the GCM-generated climate change scenario and the base 

case scenario, for the 1950-1999 period, as resulting from the changed climate. Problems of linkage, with this methodology, between hydrology models and the GCMs are outlined in the subsection, GCM Linkage Problems, on page 5. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 22
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 23

Great Lakes Physical Process Models 

The Great Lakes Environmental Research Laboratory developed, calibrated, and verified conceptual model-based techniques for simulating hydrological processes in the Laurentian Great Lakes 

(including Georgian Bay and Lake St. Clair, both as separate entities). GLERL integrated the 

models into a system to estimate lake levels, whole-lake heat storage, and water and energy balances for forecasts and for assessment of impacts associated with climate change (Croley 1990, 

1993a,b; Croley and Hartmann 1987, 1989; Croley and Lee 1993; Hartmann 1990; Lofgren et 

al. 2002). These include models for rainfall-runoff [121 daily watershed models (Croley 1982, 

1983a,b; Croley and Hartmann 1984)], over-lake precipitation (a daily estimation model), onedimensional (depth) lake thermodynamics [7 daily models for lake surface flux, thermal structure, 

and heat storage (Croley 1989a,b, 1992a; Croley and Assel 1994)], channel routing [4 daily models for connecting channel flow and level, outlet works, and lake levels (Hartmann 1987, 1988; 

Quinn 1978)], lake regulation [a monthly plan balancing Lakes Superior, Michigan, and Huron 

(International Lake Superior Board of Control 1981, 1982) and a quarter-monthly plan balancing 

Lake Ontario and the St. Lawrence Seaway (International St. Lawrence River Board of Control

1963)], and diversions and consumptions (International Great Lakes Diversions and Consumptive Uses Study Board 1981). Basin runoff, over-lake precipitation, and lake thermodynamics 

models are described in this chapter; results are presented in the next chapter. 

Runoff Modeling 

The GLERL Large Basin Runoff Model (LBRM) is an interdependent tank-cascade model, which 

employs analytic solutions of climatologic considerations relevant for large watersheds (Croley

1983a,b). It consists of moisture storages arranged as a serial and parallel cascade of "tanks" to 

coincide with the perceived basin storage structure of Figure 2. Water enters the upper soil zone 

tank and flows from the upper to the lower soil zone and surface storage tanks, from the lower to 

the groundwater and surface tanks, from the groundwater to the surface tank, and from the surface tank out of the watershed. 

Snowmelt and Infiltration. Water enters the snowpack, if present, and some then infiltrates into 

the upper soil zone based on degree-day determinations of snowmelt and net supply: 

m T

a DD T

p a

s a

= ≤

= >

0 0

0

, ,

, (1) 

where mp = daily potential snowmelt rate (m3 d-1); as = proportionality constant for snowmelt per 

degree-day (m3

 °C-1 d-1]); Ta = air temperature, estimated as the average of the daily maximum 

and minimum air temperatures (°C); and DD = degree-days per day (°C d d-1), the integral of air 

temperature with time over those portions of the day when it is positive. Since the diurnal fluctuation of air temperature is unknown, a triangular distribution is used (to approximate an expected sinusoidal variation) for computation ease. The resulting expression for degree-days is: 

( )

max

2

max

min max

max min

min

0, 0,

, 0 , 2

, 0 a

DD T

T T T

T T

T T

= ≤

= << −

= ≤

 (2) 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 24

where Tmax = maximum daily air temperature (°C) and Tmin = minimum daily air temperature (°C). 

Actual snowmelt depends upon the snowpack: 

m m m d SNW

SNW d m d SNW

p p

p

= ≤

= >

, ,

,

0

0 0

 (3) 

where m = daily snowmelt rate (m3 d-1) and SNW0 = water content of the snowpack at the beginning of the day (m3

). Snowpack mass balance and water supply to the watershed surface can now 

be determined: 

∂

∂t

SNW p T

m T

a

a

= ≤

=− >

, ,

,

0

0

 (4) 

ns T

pm T

a

a

= ≤

=+ >

0 0

0

, ,

, (5) 

where t = time, p and ns = precipitation and net supply rates to watershed surface (m3 d-1). 

Heat Available for Evapotranspiration. The heat available for evapotranspiration is estimated empirically from the average air temperature as follows: 

Ψ = K TT ( ) a b exp (6) 

where Ψ = total heat available for evapotranspiration during the day (cal), K = units and proportionality constant (cal), and Tb = a base scaling temperature (°C). The constant, K, is determinable, given Tb, from the long-term heat balance (taken over the entire simulation): 

( )

1 1

M M

i i i wf

i i

Ψ ργ rr m d = =

∑ ∑= − (7) 

where rr = daily solar insolation at the watershed surface (cal d-1), ρw = density of water (= 106

gm m-3), γf = latent heat of fusion (= 79.7 cal gm-1), M = number of days in long-term heat balance, and the subscript, i, refers to daily values. Equation 7 conserves energy in that all absorbed 

insolation not used for snowmelt appears sooner or later as other components of the heat balance 

that determine Ψ. Daily insolation is taken as: 

rr A b b X = + 10000 b ( ) 1 2 τ (8) 

where Ab = area of the watershed (m2), τ = daily extra-terrestrial solar radiation (langleys d-1), b1

and b2 = constants, and X = daily ratio of hours of bright sunshine to maximum possible hours of 

bright sunshine, estimated from daily air temperatures: 

X TT = − MIN[ ] ( ) max min / ,. 15 10 (9) 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 25

While calculations for ns and Ψ are performed on a daily basis, the mass balance computations 

(following) are performed on an n-day basis (n = 1, 7, and 28-31 are typical). The net supply and 

energy available for evapotranspiration are summed over the n-day periods prior to the mass balance: 

ns

n

ns a i

i

n

= =

∑

1

1

 (10) 

Ψ Ψ a i

i

n

= =

∑

1

(11) 

where nsa = average net supply rate for n days (m3 d-1), Ψa = accumulated energy available for 

evapotranspiration over n days (cal), and n = number of days in the mass balance computation 

periods (n = 1 in this study). The subscripts refer to daily values within the computation period. 

Infiltration. Infiltration is taken as instantaneously proportional to the supply rate and to the areal 

extent of the unsaturated portion of the upper soil zone (partial-area infiltration concept). 

f ns USZC USZM USZC ( ) = − a (12) 

where f = infiltration rate (m3 d-1), USZC = capacity of the upper soil zone (m3), and USZM = 

content of upper soil zone (m3

). The difference between the net supply rate and infiltration is surface runoff in Figure 2. 

Evapotranspiration. Consider all incoming heat to be released by the watershed surface by ignoring heat storage and the energy advected by evaporation or transpiration. The release consists of 

short-wave reflection, atmospheric heating (the resultant of net long wave exchange, sensible heat 

exchange, net atmospheric advection, and net hydrospheric advection), and evaporationtranspiration (referred to herein jointly as evapotranspiration). The total heat available for 

evapotranspiration over a day is composed of the heat actually used for evapotranspiration and 

that used for atmospheric heating. At any instant, the rate of evapotranspiration, e, is proportional to the amount of water available, Z (reflecting both areal coverage and extent of supply), 

and to the rate of nonlatent heat released to the atmosphere, ∂Hs/∂t (atmospheric heating): 

e Ze e ( ) H

t p p

s = = β w v

∂

∂ , ρ γ (13) 

where e = evapotranspiration rate (m3 d-1), β = partial linear reservoir coefficient (m-3), Z = volume of water in storage (m3

), ep = rate of evapotranspiration, respectively (m3 d-1), still possible 

and γv = latent heat of vaporization (596 - 0.52 Ta cal gm-1). This agrees with existing climatologic and hydrological concepts for evapotranspiration opportunity. 

Over large areas, climatic observations suggest that actual evapotranspiration affects temperatures, wind speeds, humidities, and so forth, and hence it affects the potential evapotranspiration 

(evapotranspiration opportunity or capacity); the heat used for evapotranspiration reduces the op-
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 26

portunity for additional evapotranspiration (complementary evapotranspiration and evapotranspiration opportunity concept). This concept is modified here by considering that, for short time periods, the total amount of energy available for evapotranspiration, Ψ, during the time period is 

split into that used for evapotranspiration and that used for atmospheric heating. From (13), for 

the daily time period, 

Ψ = + ++ + H EEE E s wv u l g s ρ γ ( ) (14) 

where Hs = nonlatent heat released to the atmosphere during the day (cal) and Eu, El, Eg, and Es = 

evapotranspiration from the upper soil zone, lower soil zone, groundwater, and surface storages 

(m3

), respectively. The evaporation from stream channels and other water surfaces (surface zone) 

in a large basin is very small compared to the basin evapotranspiration; groundwater evapotranspiration is also taken here as being relatively small. 

Mass Conservation. Percolation from the upper zone enters the lower soil zone, and deep percolation from the lower zone enters the groundwater zone; see Figure 2. Lateral flows from these 

zones of surface runoff, interflow, and groundwater flow, respectively, enter the surface storage 

zone which represents surface waters that ultimately flow from the basin. These flow rates are 

taken as instantaneously proportional to their respective storages (linear-reservoir flow concept). 

The mass balances for snowpack, upper and lower soil zones, groundwater, and surface water use 

these physically-based concepts, in the cascade of Figure 2, to form a set of simultaneous ordinary 

linear differential equations whose joint solution depends upon the relative magnitude of all parameters, inputs, and system states (storages) pictured in Figure 2. 

∂

∂ α β t

USZM ns USZM

USZC = − a per eu p USZM e USZM 



 

 1  − − (15) 

∂

∂ α ααβ t

LSZM USZM LSZM LSZM e LSZM = −−− per dp el p int (16) 

∂

∂ α αβ t

GZM LSZM GZM GZM = −− dp gw eg (17) 

∂

∂ α α αβ t

SS ns USZM

USZC

LSZM GZM SS e SS = + + −− a gw sf es p int (18) 

Q SS t = sf ∫ α ∂

0

∆

 (19) 

where αper = percolation coefficient (d-1), βeu = upper zone evapotranspiration coefficient (m-3), 

αint = interflow coefficient (d-1), LSZM = content of lower soil zone (m3), αdp = deep percolation 

coefficient (d-1), βel = lower zone evapotranspiration coefficient (m-3), αgw = groundwater coefficient (d-1), GZM = content of groundwater zone (m3

), βeg = groundwater zone evapotranspiration 

coefficient (m-3), αsf = surface outflow coefficient (d-1), SS = content of surface storage zone (m3

), 

βes = surface zone evapotranspiration coefficient (m-3), Q = basin outflow volume for n days (m3), 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 27

and ∆ = n times d. The value of ep is determined by simultaneous solution of (15)-(19) and the 

following complementary relationship between actual evapotranspiration and that still possible 

from atmospheric heat, derived from (13) and (14): 

[ ] e USZM LSZM GZM SS e t p eu el eg es p a w v + + ++ = ( ) ( ) ∫ β β β β ∂ ργ Ψ

∆

0 (20) 

Analytical Solution. In the analytical solution, results from one storage zone are used in other 

zones where their outputs appear as inputs. There are 30 different analytic results, depending 

upon the relative magnitudes of the inputs (ns), the initial conditions (USZM0, LSZM0, GZM0, SS0, 

SNW0), and the model parameters (Tb, as, αper, βeu, αint, αdp, βel, αgw, and αsf) in (15)-(19) (note 

that βeg and βes are taken as zeroes). Complete analytic solutions for all possible ranges of values 

are available (Croley 1982). Since the inputs and initial storages each day change from day to 

day, the appropriate analytic result, as well as its solution, varies with time; mathematical continuity between solutions is preserved however. Small parameter values for a tank outflow imply 

small releases and large storage volumes; large values imply small storages and outflows nearly 

equal to inflows. The differential equations for the mass balances can be applied over any time 

increment by assuming that the input (precipitation and snowmelt) and heat available for 

evapotranspiration are uniform over the time increment. Thus, the resolution of the equations is 

limited only by the intervals over which precipitation and temperature data are available; numerical solutions are unnecessary so that approximation errors are avoided. Furthermore, solutions 

may proceed for either flow rates or storage volumes directly. The mass-balance computation 

interval must be greater than or equal to the interval for which meteorological data are available. 

Application. The model is applied to daily data with either a fixed 1-d or a fixed 7-d mass-balance 

computation interval. Input and heat available for evapotranspiration are combined on a daily basis and summed over the interval as input to the mass-balance computations. The model is applied to monthly data with a variable mass-balance computation interval. The interval may represent 28 to 31 d, depending on the month and year. Input and heat available for evapotranspiration 

are computed over the same monthly interval. Again, the 1-d mass-balance computation interval 

was used herein. Data requirements include initial storage values, daily maximum and minimum 

air temperatures, daily precipitation, and for comparison purposes, daily basin outflow. Other 

data requirements are easily met. The mid-monthly extra-terrestrial solar radiation (from which 

daily values are interpolated) and the empirical constants, b1 and b2, are available in standard climatologic summaries. Watershed area is also required. 

For application of the LBRM to a Great Lakes drainage basin, the basin is first divided into subbasins draining directly to the lake (there are 121 subbasins in the entire Great Lakes basin). The 

meteorological data from typically 150-300 stations about and in the subbasins are combined 

through Thiessen weighting to produce areally-averaged daily time series of precipitation and 

minimum and maximum air temperatures for each subbasin. Weights are determined for each day 

of record, if necessary, since the data collection network changes frequently as stations are added, 

dropped, and moved or fail to report from time to time. This is feasible through the use of an algorithm for determining a Thiessen area-of-influence about a station by its edge [Croley and 

Hartmann, 1985]. Records for all "most-downstream" flow stations are combined by aggregating 

and extrapolating for ungaged areas to estimate the daily runoff to the lake from each subbasin. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 28

Thus, the LBRM is applied in a "distributed-parameter" application by combining model outflows 

from each of the subbasins to produce the entire basin runoff. 

By combining the meteorological and hydrological data for all subbasins to represent the entire 

basin, the LBRM may be calibrated in a lumped-parameter application to the entire basin at one 

time. Although the application of lumped-parameter models to very large areas necessarily fails 

to represent areal distributions of watershed and meteorological characteristics, spatial filtering 

effects tend to cancel data errors for small areas as the areas are added together. Distributedparameter applications, in which the LBRM is calibrated for each subbasin and model outflows 

are combined to represent the entire basin, make use of information that is lost in the lumpedparameter approach; the integration then filters individual subbasin model errors. 

There are five variables to be initialized prior to modeling: SNW, USZM, LSZM, GZM, and SS. 

While the initial snow pack, SNW0, is easy to determine as zero during major portions of the year, 

these variables are generally difficult to estimate. If the model is to be used in forecasting or for 

short simulations, then it is important to determine these variables accurately prior to use of the 

model. If the model is to be used for calibration or for long simulations, then the initial values are 

generally unimportant. The effect of the initial values of all storages except GZM diminishes with 

the length of the simulation and after 1 year of simulation, the effects are nil from a practical point 

of view. Some applications have groundwater parameters that allow initial GZM values to persist. 

Calibrations are repeated with initial conditions equal to calculated long-term averages until the 

averages do not change, to avoid arbitrary initial conditions when their effects persist. 

Calibration. GLERL calibrates the LBRM for each subbasin with 30 years of daily weighted climatologic data. The nine parameters are determined (Croley and Hartmann 1984) by searching 

the parameter space systematically, minimizing the root mean square error between model and 

actual outflows for each parameter, selected in rotation, until all parameters converge within two 

significant digits. Comparisons to other models (Croley 1983a) and climatology (Croley and 

Hartmann 1984) show the LBRM is superior for estimates of runoff volumes from large basins. 

The LBRM captures a "realism" in its structure that has several advantages over other models. 

Basin storages, modeled as "tanks", are automatically removed as respective parameters approach 

their limits. Thus, the structure of the model changes within a calibration. This is achieved without the use of "threshold" parameters in the model since physical concepts are used which avoid 

discontinuities in the goodness-of-fit as a function of the parameters; these concepts appear especially relevant for large-basin modeling. Because the "tanks" relate directly to actual basin storages, initialization of the model corresponds to identifying storages from field conditions which 

may be measured; interpretations of a basin's hydrology then can aid in setting both initial and 

boundary conditions. The tanks in Figure 2 may be initialized to correspond to measurements of 

snow and soil moisture water equivalents available from aerial or satellite monitoring. Snow water equivalents are used in Lake Superior applications (Gauthier et al. 1984). 

The LBRM calibration periods generally cover 1965-1982 depending upon flow data availability. 

Tables 5-11 present the LBRM calibrated parameters. Table 12 presents overall calibration results for the distributed-parameter applications. The LBRM was also used in forecasts of Lake 

Superior water levels (Croley and Hartmann 1987), and comparisons with climatic outlooks 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 29

showed the runoff model was very close to actual runoff (monthly correlations of water supply 

were on the order of 0.99) for the period August 1982 - December 1984 which is outside of and 

wetter than the calibration period (Croley and Hartmann 1986). The model also was used to 

simulate flows for the time period 1956-63, outside of the period of calibration. The correlation 

of monthly flow volumes between the model and observed during this verification period are also 

contained in Table 12. They are a little lower than the calibration correlations but quite good except for Lakes Superior and Huron (there were less than two thirds as many flow gages available 

for 1956-63 as for the calibration period for these basins). 

Studies on the Lake Ontario basin (Croley 1982, 1983b) show that the simple search algorithm 

described herein does not give unique optimums for calibrated parameter sets because of synergistic relationships between parameters. However, the calibration procedure does show a high degree of repeatability for recalibrations with different starting values, and consistent parameter values are obtained for subbasins with similar hydrological characteristics. On the other hand, the 

non-uniqueness of calibrated parameters was demonstrated by recalibrating for a synthetic data 

set. The model was calibrated for the entire Lake Superior basin and then used to simulate outflows to create a new data set for calibration. Subsequent calibration started with a very different 

initial parameter set and yielded an "optimum" parameter set different from the original with a 

relatively poor goodness-of-fit. If the original parameter set had been unique, the parameter values produced from the recalibration to the synthetic data set should have been the same as the parameters used to create that data set. This illustrates the non-uniqueness of the parameters, the 

importance of the starting values used in the search, and the problems inherent in searching the 

parameter space. Additionally, some components of the LBRM (such as linear reservoirs) are 

more likely to adequately represent their processes in the real world than others (such as degreeTable 5. Large Basin Runoff Model Parameters for the Lake Superior Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 3.0 .22×10+8 .30×10+0 .59×10+2 .21×10-9 .60×10-2 .10×10-9 .35×10-1 .86×10-1 2.28×10+15

2 7.2 .94×10+7 .12×10+3 .10×10-5 .10×10+0 .76×10-1 .79×10-8 .33×10-1 .23×10+2 4.06×10+16

3 4.7 .11×10+8 .23×10+1 .19×10-7 .39×10-1 .30×10-1 .32×10+4 .30×10-1 .22×10+0 6.88×10+15

4 6.0 .70×10+7 .71×10+0 .85×10-7 .11×10-9 .18×10-1 .30×10-8 .67×10+0 .22×10+0 1.38×10+16

5 6.3 .92×10+7 .23×10+2 .12×10-9 .40×10+1 .63×10+1 .26×10+1 .14×10-1 .26×10+0 2.24×10+16

6 4.5 .85×10+7 .54×10+0 .48×10-7 .21×10-9 .27×10+0 .95×10-7 .58×10-1 .43×10+0 5.49×10+15

7 5.2 .38×10+7 .10×10+1 .70×10-7 .11×10-1 .24×10-2 .35×10-8 .85×10-2 .17×10+0 5.95×10+15

8 9.2×10+9 .10×10+10 .14×10+2 .45×10-7 .10×10-9 .99×10-2 .78×10-9 .14×10-1 .13×10-1 1.05×10+17

9 2.3 .70×10+7 .46×10+0 .35×10+4 .14×10-2 .82×10-2 .40×10-5 .89×10-3 .75×10-1 8.39×10+13

10 2.3 .48×10+7 .46×10+0 .35×10+4 .14×10-2 .82×10-2 .40×10-5 .89×10-3 .75×10-1 6.70×10+13

11 2.3 .19×10+7 .46×10+0 .35×10+4 .14×10-2 .82×10-2 .40×10-5 .89×10-3 .75×10-1 2.90×10+13

12 5.1 .13×10+8 .68×10+0 .22×10+4 .11×10+4 .79×10+4 .90×10+0 .14×10-1 .19×10+0 2.01×10+16

13 1.1 .82×10+7 .93×10+1 .91×10+4 .11×10-2 .92×10-2 .69×10-4 .10×10-2 .95×10-1 2.00×10+10

14 3.9 .24×10+8 .47×10+1 .91×10-8 .27×10-2 .43×10-2 .20×10-9 .17×10-2 .84×10-1 1.87×10+16

15 9.7 .20×10+8 .47×10+2 .53×10-6 .20×10-1 .79×10-2 .39×10-9 .53×10+0 .11×10+0 1.59×10+17

16 5.8 .16×10+8 .54×10+0 .87×10-8 .10×10-9 .27×10-1 .33×10-8 .60×10-1 .10×10+0 4.91×10+16

17 1.8 .11×10+8 .55×10+0 .44×10-1 .32×10-2 .20×10-2 .98×10-2 .59×10-2 .71×10-1 1.02×10+14

18 1.4 .37×10+7 .34×10+0 .64×10-3 .99×10-3 .10×10-2 .96×10-1 .93×10+1 .81×10-1 7.02×10+11

19 2.0 .18×10+8 .91×10+9 .20×10-9 .79×10-2 .81×10-1 .27×10-8 .53×10-2 .52×10-2 4.23×10+14

20 2.1 .11×10+8 .61×10+0 .13×10-6 .22×10-2 .83×10-3 .57×10-7 .99×10+9 .42×10-1 1.74×10+14

21 2.0 .27×10+8 .57×10+1 .76×10+1 .42×10-2 .68×10-2 .46×10-1 .67×10-2 .11×10+0 1.18×10+14

22 3.1 .13×10+8 .54×10+0 .69×10-1 .11×10-9 .18×10+0 .63×10+0 .26×10-1 .18×10+0 4.17×10+15
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 30

day melting or complementary evapotranspiration). Parameter estimation techniques that properly weight a model's more accurate parts could improve parameter estimates. 

Over-Lake Precipitation 

The lack of over-lake precipitation measurements means that estimates typically depend on landTable 7. Large Basin Runoff Model Parameters for the Lake Huron Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 4.9 .41×10+7 .16×10+0 .29×10-6 .31×10-1 .88×10-5 .55×10-9 .75×10-1 .23×10+0 4.76×10+15

2 6.6 .93×10+6 .14×10+2 .23×10-6 .65×10-2 .82×10-2 .10×10-8 .74×10-3 .14×10+0 1.59×10+15

3 6.6 .13×10+8 .14×10+2 .23×10-6 .65×10-2 .82×10-2 .10×10-8 .74×10-3 .14×10+0 2.44×10+16

4 6.6 .47×10+7 .14×10+2 .23×10-6 .65×10-2 .82×10-2 .10×10-8 .74×10-3 .14×10+0 8.08×10+15

5 5.3 .98×10+7 .47×10+1 .32×10-6 .89×10-2 .82×10-2 .91×10-8 .42×10-2 .23×10+0 1.01×10+16

6 5.3 .14×10+7 .47×10+1 .32×10-6 .89×10-2 .82×10-2 .91×10-8 .42×10-2 .23×10+0 1.32×10+15

7 6.2 .11×10+8 .10×10+2 .20×10-6 .46×10-2 .10×10-1 .49×10-9 .96×10-3 .27×10+0 2.60×10+16

8 5.6 .79×10+7 .30×10+1 .41×10-6 .10×10-1 .55×10-6 .83×10-9 .52×10-3 .36×10+0 9.46×10+15

9 5.7 .34×10+7 .91×10-6 .66×10-3 .71×10+0 .62×10-2 .70×10-9 .30×10-1 .97×10-1 3.68×10+15

10 5.4 .45×10+8 .20×10+0 .32×10-6 .97×10-3 .20×10-1 .55×10-7 .26×10-1 .11×10+0 3.63×10+16

11 5.7 .65×10+7 .80×10-6 .27×10-4 .30×10+0 .60×10-2 .70×10-9 .41×10-1 .21×10+0 6.25×10+15

12 6.3 .81×10+7 .10×10+0 .47×10-2 .17×10-1 .99×10-6 .26×10-8 .25×10-2 .30×10+0 5.69×10+15

13 6.3 .17×10+8 .10×10+0 .47×10-2 .17×10-1 .99×10-6 .26×10-8 .25×10-2 .30×10+0 1.24×10+16

14 4.8 .19×10+8 .42×10+0 .93×10-5 .15×10-1 .86×10-6 .15×10-5 .35×10-3 .23×10+0 4.97×10+15

15 6.6 .12×10+8 .16×10+1 .13×10-1 .19×10-1 .95×10-6 .76×10-2 .80×10-1 .73×10+0 6.83×10+15

16 5.3 .30×10+8 .16×10+1 .22×10-6 .12×10-1 .53×10-2 .50×10-8 .11×10-1 .17×10+0 1.21×10+16

Table 6. Large Basin Runoff Model Parameters for the Lake Michigan Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 4.5 .36×10+7 .25×10+0 .16×10-6 .11×10+0 .25×10+0 .10×10-9 .50×10-2 .58×10-1 2.83×10+15

2 4.5 .94×10+7 .25×10+0 .16×10-6 .11×10+0 .25×10+0 .10×10-9 .50×10-2 .58×10-1 6.97×10+15

3 7.1 .30×10+7 .10×10+2 .99×10-6 .47×10-1 .25×10-1 .86×10-8 .12×10-1 .69×10+0 1.08×10+16

4 7.1 .33×10+7 .10×10+2 .99×10-6 .47×10-1 .25×10-1 .86×10-8 .12×10-1 .69×10+0 1.20×10+16

5 5.2 .50×10+7 .72×10+0 .12×10-6 .92×10-2 .90×10-7 .26×10-8 .33×10-1 .11×10+0 7.48×10+15

6 5.1 .52×10+7 .29×10+0 .11×10-6 .10×10-4 .68×10-1 .83×10-1 .53×10-1 .96×10-1 7.66×10+15

7 3.9 .24×10+8 .32×10+1 .11×10-7 .74×10-2 .46×10-2 .15×10-8 .98×10-3 .96×10-1 9.74×10+15

8 4.7 .77×10+7 .17×10+1 .12×10-6 .80×10-2 .62×10-2 .63×10-8 .52×10-2 .12×10+0 5.53×10+15

9 5.7 .71×10+7 .35×10+1 .29×10-6 .89×10-2 .10×10-1 .51×10-8 .34×10-2 .12×10+0 9.42×10+15

10 6.0 .33×10+7 .11×10+0 .18×10+2 .38×10-5 .40×10-5 .10×10+2 .64×10-1 .22×10+0 4.43×10+15

11 9.4 .12×10+10 .27×10+3 .43×10-6 .10×10-1 .91×10-7 .25×10-9 .40×10+0 .21×10+0 1.78×10+17

12 5.6 .78×10+7 .13×10+1 .20×10+2 .18×10-1 .95×10-6 .75×10+0 .25×10-5 .45×10+0 6.40×10+15

13 5.9 .17×10+8 .16×10+1 .19×10+0 .19×10-1 .82×10-5 .99×10-2 .98×10-5 .15×10+0 1.36×10+16

14 5.7 .70×10+7 .40×10+1 .32×10-5 .28×10-1 .34×10-1 .21×10-6 .10×10-1 .38×10+0 5.78×10+15

15 8.1 .92×10+7 .48×10+0 .39×10-6 .80×10-5 .68×10+6 .38×10+0 .22×10-1 .30×10+0 1.72×10+16

16 8.3 .53×10+8 .17×10+2 .47×10-7 .86×10-1 .24×10+0 .39×10-7 .14×10-1 .13×10+0 8.19×10+16

17 5.6 .10×10+9 .84×10+6 .17×10-6 .42×10-1 .50×10-1 .13×10-6 .17×10-1 .26×10+2 2.03×10+15

18 8.5 .26×10+8 .89×10+1 .34×10-6 .11×10-1 .11×10-1 .13×10-8 .43×10-2 .18×10+0 3.88×10+16

19 5.9 .23×10+7 .11×10-4 .57×10-2 .93×10+1 .66×10+0 .11×10-3 .12×10-4 .58×10+0 1.68×10+15

20 5.9 .43×10+8 .20×10+0 .25×10-6 .10×10-2 .19×10-1 .90×10-8 .21×10-1 .57×10-1 4.01×10+16

21 4.8 .76×10+6 .50×10+1 .49×10-6 .44×10-2 .64×10-2 .51×10-9 .17×10-3 .15×10+0 3.36×10+14

22 6.0 .23×10+8 .38×10+1 .16×10-6 .57×10-2 .41×10-2 .39×10-9 .12×10-2 .13×10+0 2.76×10+16

23 4.8 .15×10+8 .50×10+1 .49×10-6 .44×10-2 .64×10-2 .51×10-9 .17×10-3 .15×10+0 8.22×10+15

24 7.5 .20×10+10 .18×10+4 .62×10-4 .60×10-2 .75×10-2 .24×10-9 .26×10-3 .76×10+1 3.82×10+16

25 4.8 .63×10+7 .50×10+1 .49×10-6 .44×10-2 .64×10-2 .51×10-9 .17×10-3 .15×10+0 3.45×10+15

26 6.4 .56×10+7 .60×10+2 .26×10-5 .22×10-1 .12×10+0 .32×10-8 .23×10-3 .51×10+2 1.82×10+16

27 6.4 .11×10+7 .60×10+2 .26×10-5 .22×10-1 .12×10+0 .32×10-8 .23×10-3 .51×10+2 4.01×10+15
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 31

based measurements and there may be differences between land and lake meteorology. Although 

gage exposures may significantly influence the results of lake-land precipitation studies (Bolsenga

1977, 1979), Wilson (1977) found that Lake Ontario precipitation estimates based on only nearshore stations averaged 5.6% more during the warm season and 2.1% less during the cold season 

than estimates based on stations situated in the lake. By using a network that also included stations somewhat removed from the Lake Ontario shoreline, Bolsenga and Hagman (1975) found 

that eliminating several gages not immediately in the vicinity of the shoreline increased over-lake 

precipitation estimates during the warm season and decreased them during the cold season. Thus, 

for the Great Lakes, where lake effects on near-shore meteorology are significant and the drainage basins have relatively low relief, the use here of all available meteorological stations throughout the basin is probably less biased than the use of only near-shore stations. Overlake precipitation is estimated via Thiessen weighting of all stations, which admittedly will more heavily weight 

near-shore stations. 

Over-Lake Evaporation 

Great Lakes hydrological research mandates the use of continuous-simulation models of daily lake 

evaporation over long time periods. Such models must be usable in the absence of water surface 

temperature and ice cover observations. They also must be physically based to have application 

under environmental conditions different than those under which they were derived. GLERL developed a lumped-parameter model of evaporation and thermodynamic fluxes for the Great Lakes 

based on an energy balance at the lake's surface (Croley 1989a,b) and on one-dimensional (vertiTable 8. Large Basin Runoff Model Parameters for the Georgian Bay Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 4.3 .16×10+8 .11×10+0 .18×10-3 .21×10-1 .83×10-6 .11×10-4 .87×10-3 .81×10-1 2.97×10+15

2 6.1 .14×10+8 .37×10+1 .20×10-6 .15×10-1 .89×10-6 .43×10-8 .20×10-2 .24×10+0 7.98×10+15

3 6.0 .21×10+8 .33×10+1 .41×10-6 .10×10-1 .77×10-2 .94×10-8 .70×10-2 .35×10+0 1.85×10+16

4 4.7 .23×10+8 .84×10+1 .46×10-6 .71×10-2 .57×10-2 .14×10-7 .13×10-3 .13×10+0 1.15×10+16

5 4.8 .41×10+8 .43×10+4 .80×10-5 .16×10-1 .74×10-2 .27×10-8 .31×10-3 .34×10+0 1.43×10+16

6 3.9 .25×10+8 .52×10+2 .59×10-4 .12×10+0 .53×10-1 .59×10-6 .38×10-5 .79×10-1 6.14×10+15

7 2.6 .16×10+9 .57×10+6 .82×10-9 .75×10-2 .58×10-2 .59×10-9 .50×10-5 .79×10-1 1.30×10+15

8 3.7 .45×10+8 .21×10+2 .22×10-7 .46×10-2 .18×10-2 .81×10-9 .85×10-3 .17×10+0 2.99×10+15

9 4.4 .46×10+8 .12×10+1 .75×10-8 .62×10-2 .35×10-3 .24×10-9 .19×10-1 .75×10-1 3.98×10+16

10 4.4 .99×10+7 .74×10+0 .34×10-6 .26×10-1 .27×10-5 .22×10-8 .46×10-1 .54×10-1 5.01×10+15

11 2.2 .22×10+8 .30×10+1 .70×10-7 .48×10-2 .22×10-2 .50×10-9 .26×10-3 .99×10-1 2.34×10+14

12 4.9 .99×10+7 .16×10+0 .29×10-6 .31×10-1 .88×10-5 .55×10-9 .75×10-1 .23×10+0 1.19×10+16

13 4.9 .29×10+7 .16×10+0 .29×10-6 .31×10-1 .88×10-5 .55×10-9 .75×10-1 .23×10+0 3.41×10+15

Table 9. Large Basin Runoff Model Parameters for the Lake St. Clair Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 6.4 .11×10+8 .97×10-1 .11×10+1 .90×10-6 .10×10-1 .98×10+0 .42×10-1 .25×10+0 1.17×10+16

2 8.2 .72×10+6 .16×10+2 .42×10-5 .10×10+0 .16×10+0 .11×10-6 .15×10-1 .31×10+1 2.85×10+15

3 8.2 .53×10+7 .16×10+2 .42×10-5 .10×10+0 .16×10+0 .11×10-6 .15×10-1 .31×10+1 1.30×10+16

4 8.2 .37×10+6 .16×10+2 .42×10-5 .10×10+0 .16×10+0 .11×10-6 .15×10-1 .31×10+1 1.31×10+15

5 8.5 .53×10+7 .11×10+0 .53×10-5 .51×10-1 .60×10-5 .86×10-7 .51×10-1 .65×10+0 5.02×10+15

6 7.8 .24×10+8 .41×10+5 .72×10+2 .31×10+0 .11×10+0 .34×10-7 .21×10-1 .28×10+0 3.96×10+16

7 6.4 .18×10+8 .45×10-1 .34×10-4 .97×10-2 .11×10-5 .51×10-8 .59×10-1 .18×10+0 1.33×10+16
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 32

cal) lake heat storage (Croley 1992a). Ice formation and loss is coupled also to lake thermodynamics and heat storage (Croley and Assel 1994). 

Thermodynamic Fluxes. The thermodynamic fluxes to and from a lake include incident shortwave radiation, qi, reflected short-wave radiation, qr and qr' (over water and over ice, respectively), evaporative (latent and advected) heat transfer, qe and qe', sensible heat transfer, qh and 

qh', precipitation heat advection, qp and qp', net long-wave radiation exchange, Ql, and surface 

flow advection, QI; see Croley (1989a,b) for details: 

q Nq i = +− [ ] 0355 0 68 1( ) 0 . . (21) 

Table 10. Large Basin Runoff Model Parameters for the Lake Erie Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 8.0 .47×10+7 .13×10+1 .67×10-6 .24×10-1 .53×10-1 .14×10-6 .14×10-1 .11×10+1 1.02×10+16

2 10. .85×10+7 .30×10+2 .57×10-5 .45×10-1 .12×10+0 .59×10-7 .17×10-1 .40×10+0 2.30×10+16

3 6.2 .23×10+7 .73×10+0 .37×10-2 .10×10-4 .17×10-1 .65×10-3 .27×10-1 .36×10+0 2.29×10+15

4 7.9 .11×10+8 .88×10-5 .95×10-2 .90×10-1 .79×10-1 .88×10-4 .10×10+0 .10×10+0 1.79×10+16

5 8.1 .42×10+7 .58×10-4 .11×10-5 .60×10+5 .99×10-1 .10×10-3 .20×10+0 .33×10+0 5.92×10+15

6 6.6 .74×10+8 .39×10-1 .45×10-7 .97×10-5 .32×10-5 .64×10-7 .49×10-1 .19×10+0 6.07×10+16

7 6.4 .90×10+7 .43×10-1 .47×10-6 .86×10-5 .61×10-5 .12×10-5 .64×10-1 .41×10+0 7.50×10+15

8 5.9 .41×10+8 .49×10-1 .12×10-5 .60×10-2 .25×10-5 .16×10-5 .60×10-1 .28×10+0 1.10×10+16

9 7.1 .12×10+8 .92×10-6 .49×10-5 .10×10-4 .30×10-5 .59×10-7 .50×10-1 .12×10+1 9.28×10+15

10 5.2 .73×10+7 .11×10+0 .29×10-6 .12×10-1 .63×10-5 .23×10-6 .59×10-1 .66×10+0 3.77×10+15

11 7.6 .57×10+7 .70×10+1 .84×10-6 .11×10+0 .57×10-1 .16×10-7 .22×10-1 .32×10+1 1.12×10+16

12 5.8 .38×10+7 .11×10+1 .12×10-5 .65×10-1 .58×10-5 .19×10-7 .29×10-1 .34×10+1 2.44×10+15

13 5.1 .60×10+7 .64×10-6 .13×10-5 .10×10-4 .30×10-5 .59×10-7 .50×10-1 .33×10+0 3.16×10+15

14 4.5 .50×10+8 .64×10-1 .23×10-5 .85×10-1 .44×10-5 .19×10-3 .61×10-1 .68×10+0 6.33×10+14

15 4.4 .79×10+7 .32×10-1 .49×10-6 .39×10-1 .54×10-5 .10×10-9 .58×10-1 .66×10+0 1.99×10+15

16 4.3 .35×10+7 .17×10+1 .11×10-5 .15×10+0 .14×10+0 .53×10-7 .24×10-1 .68×10+1 1.57×10+15

17 4.6 .80×10+7 .16×10+1 .14×10-4 .17×10+0 .20×10+0 .15×10-5 .27×10-1 .66×10+1 2.55×10+15

18 4.6 .51×10+6 .16×10+1 .14×10-4 .17×10+0 .20×10+0 .15×10-5 .27×10-1 .66×10+1 1.33×10+14

19 9.4 .31×10+8 .27×10+2 .80×10-2 .33×10+0 .40×10+0 .38×10-7 .18×10-1 .35×10+0 7.44×10+16

20 6.9 .24×10+8 .26×10+1 .28×10-5 .57×10-1 .72×10-1 .16×10-6 .13×10-1 .51×10+0 2.08×10+16

21 14. .14×10+8 .91×10+2 .11×10-3 .35×10+0 .44×10-5 .54×10-7 .75×10-1 .10×10+1 3.09×10+16

Table 11. Large Basin Runoff Model Parameters for the Lake Ontario Subbasins. 

No. Tb as αper βeu αint αdp βel αgw αsf K

oC m3

 oC-1 d-1 d-1 m-3 d-1 d-1 m-3 d-1 d-1 cal 

1 6.0 .17×10+8 .51×10-1 .44×10-4 .61×10-2 .33×10-5 .15×10-3 .24×10+0 .33×10+0 1.39×10+16

2 6.0 .97×10+7 .51×10-1 .44×10-4 .61×10-2 .33×10-5 .15×10-3 .24×10+0 .33×10+0 7.70×10+15

3 4.2 .16×10+8 .90×10-4 .56×10-7 .20×10-1 .73×10-5 .14×10-9 .67×10-1 .63×10-1 5.70×10+15

4 5.5 .43×10+7 .49×10+0 .33×10-5 .17×10-5 .19×10+0 .36×10-6 .22×10-1 .40×10+0 3.66×10+15

5 4.3 .49×10+8 .12×10+0 .19×10-7 .41×10-1 .74×10-5 .96×10-7 .29×10+0 .45×10-1 1.12×10+16

6 4.3 .70×10+7 .18×10+1 .33×10-5 .12×10+0 .87×10-1 .39×10-7 .42×10-1 .36×10+1 2.28×10+15

7 4.4 .22×10+8 .10×10-5 .11×10-7 .20×10-4 .30×10-5 .81×10-7 .50×10-1 .59×10-1 8.62×10+15

8 3.1 .18×10+8 .11×10+0 .10×10-6 .21×10-1 .14×10-5 .10×10-9 .36×10-1 .94×10-1 9.13×10+14

9 4.4 .12×10+8 .83×10+0 .55×10-1 .89×10-6 .15×10-1 .20×10-2 .79×10+2 .10×10+0 2.11×10+15

10 4.4 .17×10+8 .83×10+0 .55×10-1 .89×10-6 .15×10-1 .20×10-2 .79×10+2 .10×10+0 3.39×10+15

11 6.9 .14×10+8 .49×10+1 .59×10-1 .15×10+0 .12×10+0 .27×10-6 .22×10-1 .10×10+0 1.68×10+16

12 5.6 .77×10+8 .57×10+6 .11×10-9 .17×10-1 .49×10-2 .19×10-8 .95×10-2 .53×10+0 4.46×10+16

13 5.5 .95×10+7 .19×10+1 .23×10-4 .95×10-2 .24×10-1 .25×10-7 .71×10-2 .15×10+1 7.43×10+15

14 5.5 .84×10+7 .19×10+1 .31×10-5 .20×10-1 .28×10-1 .23×10-6 .12×10-1 .48×10+0 7.22×10+15

15 5.5 .72×10+7 .19×10+1 .31×10-5 .20×10-1 .28×10-1 .23×10-6 .12×10-1 .48×10+0 6.14×10+15
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 33

where qi = daily average unit (per unit area) rate of short-wave radiation incident to the earth's 

surface, N = fraction of the sky covered by clouds, and q0 = daily average unit rate of short-wave 

radiation received on a horizontal unit area of the Earth's surface under cloudless skies; 

q q r i = 01. (22) 

where qr = average unit reflected short-wave radiation rate from the water surface; 

e C q qU w aEw w = − ρ ρ ( ) (23) 

where ew = over-water evaporation rate, ρa = density of air, CE = bulk evaporation coefficient 

over water, qw = specific humidity of saturated air at the temperature of the water surface, q = 

specific humidity of the atmosphere over water, and U = wind speed over water; 

q CTe e v w ww = + ( ) γ ρ (24) 

where qe = average unit evaporative (latent and advected) heat transfer rate from the water surface, Cw = specific heat of water, and T = water surface temperature; 

q CC T TU h a pH a = − ρ ( ) (25) 

where qh = average unit sensible heat transfer rate to the water surface, Cp = specific heat of air 

at constant temperature, and CH = sensible heat coefficient over water; 

q CT p T ( )

CT p T

p wa f w a

wa w a

= − <°

= ≥°

γ ρ

ρ

,

,

0

0

C

C

 (26) 

where qp = average unit precipitation heat advection rate to the water surface; 

q T w ( ) ↑ = +° ε σ 27316 4. C (27) 

Table 12. Large Basin Runoff Model Calibration Statisticsa. 

Lake 

Number 

of 

Subbasins 

Mean 

1-day 

Flow 

(mm)b

Flow 

Standard 

Deviation 

(mm)b

Root 

Mean 

Square 

Error 

(mm)b

Correlation 

Calibration 

Independent 

Verification 

Superior 22 1.12 0.67 0.25 0.93 0.77 

Michigan 29 0.89 0.47 0.18 0.93 0.86 

Huron 27 1.06 0.69 0.26 0.92 0.69 

St. Clair 7 0.90 1.36 0.62 0.89 0.87 

Erie 21 1.01 1.28 0.54 0.91 0.90 

Ontario 15 1.41 1.13 0.43 0.93 0.89 

a

Statistics and calibrations generally are 1966-83; verification generally is 1956-63. 

b

Equivalent depth over the land portion of the basin.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 34

where q↑ = average unit long-wave radiation emitted by the water body, σ = Stephan-Bolzmann 

constant (5.67×10-8 W m-2 K-4), and ew = emissivity of the water surface; 

q rT ( ) a a ( ) ↓ =− + ° 1 27316 4ε σ . C (28) 

where q↓ = average unit long-wave radiation from the atmosphere absorbed by the water surface, 

ra = reflectivity of the water surface, and ea = emissivity of the atmosphere; 

Q q N qA A l w = +− − − + { } [ ] ( )( ) ( ) ↓ ↑ η η 1 1 (29) 

where Ql = average net long-wave radiation exchange rate between the entire water body and the 

atmosphere (effects of ice cover on the net long-wave exchange are ignored here), η = empirical 

coefficient relating cloudiness to atmospheric long-wave radiation, Aw = area of the open-water 

(ice-free) surface, and A = area of the ice surface; 

Q CT I ww i o = − ρ ΘΘ ( ) (30) 

where QI = daily net flow heat advection to the lake assuming inflows at surface temperatures, Θi

= sum of all surface inflows to the lake, and Θo = sum of all outflows from a lake; 

q f f f fq r n o m bi '. . . . = +++ ( ) 0 85 0 70 0 50 0 45 (31) 

where qr' = average unit reflected short-wave radiation rate from the ice pack, fn = fraction of ice 

covered with new snow, fo = fraction of ice covered with old snow, fm = fraction of ice covered 

with melting snow, and fb = fraction of ice that is bare of snow; 

e C q qU w aE w w ' ' ' '' = − ρ ρ ( ) (32) 

where ew' = over-ice evaporation rate, CE' = bulk evaporation coefficient over ice, qw' = specific 

humidity of saturated air at temperature of ice, q' = specific humidity of the atmosphere over ice, 

and U' = wind speed over ice; 

q CTe e v f w ww ' '' = ++ ( ) γγ ρ (33) 

where qe' = average unit evaporative (latent and advected) heat transfer rate from the ice pack and 

T' = ice surface temperature; 

q CC T TU h apH a ' '' ' = − ρ ( ) ' (34) 

where qh' = average unit sensible heat transfer rate to the ice pack, CH' = sensible heat coefficient 

over ice, and Ta' = temperature of the air over ice; and 

q CT p p wa w ' ' = ρ (35) 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 35

where qp' = average unit precipitation heat advection rate to the ice pack. 

Gray et al. (1973) provided (21), generalized maps of mid-monthly values from which q0 may be 

interpolated by date, and the short-wave reflection of (22) and (31). Because data are unavailable 

and because subsequent heat budgets are insensitive to their values, fn, fo, and fm are set to zero 

here and fb is set to unity. Values of over-water and over-ice meteorology (q, U, Ta, N, q', U', 

and Ta') are determined from overland values by adjusting for over-water conditions. Phillips and 

Irbe’s (1978) regressions for over-water corrections are used directly by replacing the fetch (and 

derived quantities) with averages. The bulk evaporation coefficients over water and over ice (CE

and CE') are determined similar to Quinn (1979) from over-water or over-ice (respectively) wind 

speed, air temperature, and surface temperature. The over-water and over-ice sensible heat coefficients (CH and CH') are taken equal to the bulk evaporation coefficients, respectively (Quinn

1979). The emissivities of water and air in (27) and (28) [note the reflectivity of the water surface 

in (28) is ra = 1 - ew] are taken, respectively, as 0.97, and 0.53 + 0.065 ea

1/2 where ea is the vapor 

pressure of the air (mb) after Keijman (1974). 

Heat Storage. The heat added to a lake and the heat added to the ice pack, from the surface 

fluxes, are governed by simple energy and mass balances, energy-storage relationships, and 

boundary conditions on ice growth, water temperature, and ice temperature; see Figure 13. The 

rate of change of heat storage in a lake with time is: 

( ) ∂

∂

H

t

= −−++ + + − Aq q q q q Q Q Q wi r e h p l I w (36) 

where ∂H/∂t = time rate of change of heat storage H in the lake and Qw = total heat flux between 

the water body and the ice pack. The rate of change of heat storage in the ice pack with time is: 

( ) ∂

∂

H

t

Aq q q q q Q ir e h p w

'

= −−++ + '''' (37) 

where ∂H’/∂t = time rate of change of heat storage H' in the ice pack. 

Kraus’ and Turner's (1967) mixedlayer thermal structure concept is extended to allow the determination of 

simple heat storage. Effects of past 

additions or losses are superimposed 

to determine surface temperature on 

any day as a function of heat in storage; each past addition or loss is parameterized by age. Turnovers (convective mixing of deep lower-density 

waters with surface waters as surface 

temperature passes through that at 

maximum density) can occur as a fundamental behavior of this superposiQa

Qw

C

A

D

C = Circumference of ice 

pack

D = Depth of ice pack 

A = Area of ice pack 

dA

dD

Figure 13. Conceptual Prismatic Ice Pack.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 36

tion model and hysteresis between heat in storage and surface temperature, observed during the 

heating and cooling cycles on the lakes, is preserved. Water surface temperature becomes 

(Croley 1992a): 

T fH H k km ( ) mnk n m nk n

m

k

= °+ − ≤ ≤ −≤ ≤ =398 ∑ 1 1. C MIN MIN , (38) 

where Tk = water surface temperature and Hk = heat storage in the lake k days after the last turnover, and fk,m is a "wind-aging" function, defined subsequently, relating surface temperature rise 

on day k to heat added on day m. Ice surface temperature relates to ice pack heat storage here as: 

H CV T V k ikk f k ' ' /2 = − ρ ργ ' (39) 

where Tk' = ice surface temperature on day k, Hk' = heat storage in the ice pack on day k, ρ = density of ice, Ci = specific heat of ice, Vk = volume of the ice pack on day k, and Vk' = volume of ice 

formed by freezing or melting on day k. The boundary conditions on water surface temperature 

and volume of the ice pack for every day (dropping the daily subscript) are: 

V T = ≥° 0 0 , C (40) 

T V =° ≥ 0 0 C, (41) 

These equations are satisfied by selecting the heat flux between the water and ice, Qw, appropriately. Qw, if negative, is yielded as ice forms (to keep water surface temperature from going below freezing) and, if positive, is used in melting ice (to keep water surface temperature at freezing 

as long as there is ice present). The boundary conditions on ice surface temperature and volume 

of the ice pack for every day (dropping the daily subscript) are: 

TT V T a a ' , = > ≤° 0 0 and C (42) 

T VTa ' , =° = >° 0 00 C or C (43) 

where Ta = over-ice air temperature. The volume of the ice pack, V, and the volume of ice 

formed by freezing or melting, V', are related: 

∂

∂

∂

∂

V

t

V

t

= +− S E ' (44) 

where S = volumetric rate of snow falling on the ice and E = volumetric rate of evaporation from 

the ice. The "wind-aging" function, fk,m, is: 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 37

,

, ,

,

,

,

,

2 / 2 , MIN , 1 /

1 2 2 , MIN , MAX , 1 / 1/

1 2 , MAX , 1 /

k m c

km km

w w km c

c c

km c

w w km c c

c

c km

w wc c

M F V f MF CM V F

V V F MV

C M VF VF

V V M

CV V F

ρ

ρ

ρ

−  

= <     +

   = ≤<       + +

  = ≤     +

 (45) 

where Vc = volume (capacity) of the lake and Mk,m = mixing volume size in the lake, on day k, of 

the heat added on day m (a function of accumulated wind movement, Wj, from day m through day 

k), 

M V a bW km e j

j m

k

, =+ − exp





 



 











 = 

−

1 ∑

1

 (46) 

Also, a, b, F, and Ve = empirical parameters to be determined in a calibration to observed data. Ve

is interpreted as the "equilibrium" volume approached as a limit (in a sufficiently deep lake) since 

the effects of wind mixing at the surface diminish with distance from the surface. F is interpreted 

as the mixing volume at which a heat addition is fully mixed throughout. Parameters a, b, and F

are defined for water temperatures above 3.98°C (“turnover” temperature of water at maximum 

density) and are replaced by a', b', and F', respectively, for water temperatures below 3.98°C. 

Details for the flux terms in (36) and (37) are presented by Croley (1989a,b). Derivation details 

of (38), (45), and (46) are available elsewhere (Croley 1992a). 

Ice Pack Growth. In (39), linear vertical temperatures are used through the ice pack from T' on 

the surface to 0°C on the bottom, similar to Green and Outcalt (1985). Differentiating (4) and 

ignoring small terms, 

∂

∂ ρ

∂

∂ ρ γ

∂

∂

H

t

C V T

t

V

t i f

' ''

≅ − 1

2 (47) 

Thus, the heat change is split between a temperature change in the ice pack and a volume change 

due to melting or freezing. Comparing (37) and (47), note the temperature change in (47) is 

taken here as resulting from a portion of the heat added from (or lost to) the atmosphere [A (qi - 

qr' - qe' + qh' + qp')]. The remainder of that heat is identified as Qa: 

Q Aq q q q q CV ( ) T

t a ir e h p i = −−++ − '''' ' 1

2 ρ

∂

∂ (48) 

This heat (Qa) and all of the heat added from the water body, Qw, then result in changes to the ice 

pack volume (freezing or melting); from (37), (44), (47), (48): 

Q Q V

t

V

t aw f f + =− =− − + S E 



 

 ρ γ  ∂

∂ ρ γ

∂

∂

' (49) 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 38

Consider a prismatic ice pack with surface area A and depth (or thickness) D. The heat exchange 

between the atmosphere and the ice pack available for freezing or melting, Qa, is taken as resulting in either melt (along the entire atmosphere-ice surface) or freezing (along the entire water-ice 

surface). The heat exchange between the water body and the ice pack, Qw, is taken as resulting in 

changes along only the water/ice surface (either melt or freezing). After simplification (Croley 

and Assel 1994), 

( ] ( ) ( )( ) ∂

∂ ργ

D

t

Q

A xD I Q Q

A xD I Q Q

A xD

S

A

E

A xD

a

w

a

a

a

a

w

wf a

= − + − + − +













+ −

+ −∞ ∞ , , 0 0

1 (50) 

( ] ( ) ( ) ( ) ∂

∂ ργ

A

t

x Q

A xD I Q x Q

A xD I Q x Q

A xD

x E

A xD

w a

w

a

a a

a

a

w w

w f

a

a

= − + − + − +













− + −∞ ∞ , , 0 0

1 (51) 

x A a a = τ 1 2/ (52) 

x A w w = τ 1 2/ (53) 

where I(.,.)(x) = indicator function (equal to unity if the quantity in parentheses, x, is within the indicated interval and equal to zero if not), τa and τw = empirical coefficients depending upon ice 

pack shape, the ratios of vertical to lateral changes along the atmosphere-ice interface and along 

the water-ice interface, and the buoyancy of ice. The change in total ice volume is, from (50) and 

(51): 

( )

( )

∂

∂

∂

∂

∂

∂

∂

∂

ρ γ

V

t

A D

t

A D

t

D A

t

Q Q SE a w

f

= =+

=− − + −

1 (54) 

Note, (49) and (54) agree. 

Equations (36)-(48), (50)-(54), and those for the component fluxes, (21)-(35), may be solved simultaneously to determine the heat storage, the water and ice surface temperatures, and the ice 

pack extents. The Lake Evaporation and Thermodynamics Model is pictured schematically in 

Figure 14. 

Calibration Procedure. Two calibrations are involved in applying the model in a particular setting. 

The first determines the first eight parameters (a, b, F, a', b', F', Ve, and h). The first seven parameters relate to superposition heat storage (Croley 1992a) and the eighth parameter, h, reflects 

the effect of cloudiness on the atmospheric net long-wave radiation exchange (Croley 1989a,b). 

This calibration minimizes daily water surface temperature root mean square error (RMSE) by 

using methods described elsewhere (Croley and Hartmann 1984). Meteorology data for 1948-

1985 and water surface temperature data on each of the Great Lakes, except Lake Michigan, 

were taken from airplane and satellite measurements, extended through August 1988, and prepared as described by Croley (1989a,b). Water surface temperature data for Lake Michigan from 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 39

1981 through 1985 were gleaned from areal maps prepared at the National Weather Service's Marine Predictions Branch (B. Newell, personal communication, 1990) and extended through August 

1988 also. The second calibration determines the two parameters (τa and τw) that minimize daily 

ice cover RMSE with these same calibration techniques. Lake-averaged ice cover for model calibration was calculated from GLERL's digital ice cover data base (Assel 1983). In most cases, less 

than 100% of a lake was observed on any given date. If less than 70% of the Lake Superior surface was observed, the ice cover for that date was not included in the model calibration. A subjective estimate of lake-averaged ice cover was made for the other Great Lakes if the data were 

insufficient. 

Parameters are determined, in both cases, in automated systematic searches of the parameter 

spaces to minimize the RMSE between simulated and model outputs. Each parameter, selected in 

rotation, is searched until all parameter values converge to four digits, instead of searching only 

until the RMSE stabilizes. This simple search algorithm does not give unique optima for calibrated parameter sets because of synergistic relationships between parameters which allow parameter compensations to occur. However, the model concepts have been carefully chosen so 

that the parameters have physical significance; this allows them to be interpreted in terms of the 

thermodynamics they represent. Initialization of the model corresponds to identifying values from 

field conditions which may be measured; interpretations of a lake's thermodynamics then can aid 

in setting both initial and boundary conditions. 

Figure 14. Lake Evaporation and Thermodynamics Model Conceptual Schematic. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 40

Prior to calibration or model use, the (spatial) average temperature-depth profile in the lake and 

the ice cover must be initialized. While the ice cover is easy to determine as zero during major 

portions of the year, the average temperature-depth profile in the lake is generally difficult to determine. If the model is to be used in forecasting or for short simulations, then it is important to 

determine these variables accurately prior to use of the model. If the model is to be used for calibration or for long simulations, then the initial values are generally unimportant. The effect of the 

initial values diminishes with the length of the simulation, and after 2-3 years of simulation, the 

effects are nil from a practical point of view. 

Empirical coefficients of the evaporation, heat storage, and ice sub-models were calibrated in an 

iterative process that used the two calibrations sequentially in rotation. GLERL used independent 

data (lake-averaged daily surface temperature for the lake thermodynamics and heat storage submodels and lake-averaged daily ice cover for the lake ice cover sub-model). First they minimized 

the RMSE of daily water surface temperature by calibrating lake thermodynamics model parameters and holding the parameters for the ice cover sub-model constant. they then held lake thermodynamics model parameters constant and calibrated the parameters of the ice cover sub-model 

to minimize the RMSE of daily ice cover. Then they repeated the process until the RMSEs for 

both water surface temperatures and ice cover did not significantly reduce. 

Application. The results of the parameter calibration, as well as a few statistics on each of the 

Great Lakes, are summarized in Table 13. Statistics from the calibration and from an independent 

verification period are presented in Table 14. Turnovers (convective mixing of deep lowerdensity waters with surface waters as surface temperature passes through that at maximum density) occur as a fundamental behavior of GLERL's thermodynamic and heat storage model. Hysteresis between heat in storage and surface temperature, observed during the heating and cooling 

cycles on the lakes, is preserved. The model also correctly depicts lake-wide seasonal heating and 

cooling cycles, vertical temperature distributions, and other mixed-layer developments. There is 

good agreement between the actual and calibrated-model water surface temperatures; the RMSE 

is between 1.1-1.6°C on the large lakes [within 1.1-1.9°C for an independent verification period, 

1966-79 (Croley 1989a,b, 1992a)]. The RMSE for ice concentrations is between 12 and 23% for 

Table 13. Lake Evaporation and Thermodynamics Model Constants and Parameters.

 Lake 

 Superior Michigan Huron Georgian Erie Ontario 

Surface area, km2 82,100 57,800 40,640 18,960 25,700 18,960 

Volume, km3 12,100 4,920 2,761 779 484 1,640 

Average depth, m 147 85.1 67.9 41.1 18.8 86.5

a 6.298×10+0 7.290×10+0 6.460×10+0 1.585×10+0 2.820×10+0 7.710×10+0

b, m

-1 s 3.298×10-3 2.599×10-3 2.810×10-3 5.473×10-3 5.430×10-3 2.800×10-3

F, km3

 3.273×10+3 5.100×10+2 4.890×10+3 1.101×10+3 1.000×10+2 2.000×10+2

a' 2.019×10+0 1.158×10+0 3.829×10+0 1.471×10+0 2.610×10+0 4.000×10+0

b', m

-1 s 3.795×10-3 2.301×10-3 3.890×10-3 1.103×10-2 5.600×10-3 5.110×10-3

F', km3

 5.113×10+3 4.000×10+3 6.789×10+3 8.943×10+2 1.000×10+2 4.600×10+2

Ve, km3

 1.200×10+4 5.006×10+3 8.010×10+3 9.748×10+2 8.490×10+2 2.000×10+3

h 1.299×10+0 1.068×10+0 1.150×10+0 1.223×10+0 1.290×10+0 1.200×10+0

τa 9.011×10+8 9.001×10+8 9.119×10+8 9.279×10+8 9.988×10+8 9.010×10+8

τw 8.002×10+5 2.003×10+5 1.080×10+6 4.437×10+5 9.202×10+5 8.001×10+4
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 41

the joint calibration-verification period. There is also good agreement with 8 years of bathythermograph observations of depth-temperature profiles on Lake Superior and 1 year of independently-derived weekly or monthly surface flux estimates on Lakes Superior, Erie, and Ontario (2 

estimates). 

Calibration Issues. There were several problems in calibrating the model. First, it appears that 

the models are close to being over-specified in terms of the number of parameters used; i.e., there 

appear to be almost too many degrees of freedom allowed for the data sets used in the calibrations. The result is that the optimums are not unique and it is not possible to determine meaningTable 14. Lake Evaporation and Thermodynamics Model Calibration Statistics. 

 Lake 

 Superior Michigan Huron Georgian Erie Ontario 

CALIBRATION PERIOD STATISTICS 

Water Surface Temperatures (1980-1988)a

Means Ratiob

 1.00 1.01 0.98 1.01 1.03 0.99 

Variances Ratioc

 1.01 0.98 0.95 1.02 1.08 0.99 

Correlationd

 0.98 0.97 0.98 0.99 0.99 0.98 

R.M.S.E.e

 1.13 1.56 1.33 1.10 1.58 1.43 

Ice Concentrations (1960-1988)f

Means Ratiog

 0.92 0.72 0.70 0.98 1.15 0.39 

Variances Ratioh

 1.24 1.02 1.67 1.62 1.09 0.63 

Correlationi

 0.76 0.83 0.73 0.77 0.89 0.54 

R.M.S.E.j

 23.4 12.4 26.0 21.5 19.0 15.4 

VERIFICATION PERIOD STATISTICS 

Water Surface Temperatures (1966-1979)k

Means Ratiob

 0.96 1.03 0.98 1.05 0.94 

Variances Ratioc

 1.10 0.95 1.00 1.10 0.97 

Correlationd

 0.97 0.99 0.98 0.98 0.96 

R.M.S.E.e

 1.09 1.10 1.34 1.91 1.92 a

Data between 1 January 1980 and 31 August 1988 for all lakes except Michigan and between 1 January 

1981 and 31 August 1988 for Lake Michigan, with an initialization period for all lakes except Georgian 

Bay starting 1 January 1948 and 1 January 1953 for Georgian Bay. 

b

Ratio of mean model surface temperature to data mean (oC/oC). 

c

Ratio of variance of model surface temperature to data variance. 

d

Correlation between model and data surface temperature. 

e

Root-mean-square-error between model and data surface temperatures in oC. 

f

Data between 1 January 1960 and 31 August 1988 for all Great Lakes except Superior and between 1 

March 1963 and 31 August for Lake Superior, with an initialization period for all lakes starting 1 January 

1958. 

g

Ratio of mean model ice concentration to data mean. 

h

Ratio of variance of model ice concentration to data variance. 

i

Correlation between model and data ice concentration. 

j

Root-mean-square-error between model and data ice concentrations in %. 

k

Data between 1 January 1966 and 31 December 1979 for all lakes except Michigan with an initialization 

period for all lakes except Georgian Bay starting 1 January 1948 and 1 January 1953 for Georgian Bay.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 42

ful values of any additional parameters. Parameter compensation exists so that changes in one 

parameter can be offset by changes in other parameters with little change in the RMSE of the calibration. This made it difficult to determine an ice break-up model, not presented here, which had 

an additional three parameters. GLERL had considered ice breakage and rejoining by developing 

a differential equation for the rate of change with time of the number of ice pieces as a function of 

wind stress, melting, and refreezing. GLERL could not meaningfully calibrate this addition to the 

ice model with the ice cover data sets GLERL had, and so GLERL eliminated ice break-up from 

the model presented here. Perhaps when other parameters are reduced through model reformulations in calibrations at a later date, it will be possible to model and calibrate for ice break-up in a 

meaningful manner. 

Second, optimizing parameters with regard to two objectives (minimizing RMSEs associated with 

water surface temperatures and ice cover) does not produce the same parameter sets. There 

seems to be a trade-off between the two objectives at times and RMSE of water temperatures decreases at the expense of ice cover RMSE and vice-versa. 

The model has ten parameters calibrated to match water surface temperatures and ice cover. 

Seven of them are defined in the superposition heat storage submodel. The number of empirical 

model parameters could perhaps be reduced by use of other one-dimensional mixed-layer heatstorage models (McCormick and Meadows 1988; Hostetler and Bartlein 1990). The critical limitation of such models for long-term hydrological forecasting and simulation is the lack of representative or accurate hourly hydrometeorological data over long periods. Secondarily, computer 

time can be excessive for such models in forecast or multi-year simulation environments. 

Models Validity and Applicability 

Although GLERL uses a daily resolution of data with their models, basin-wide processes of runoff, over-lake precipitation, and lake evaporation (described with models here) respond discernibly to weekly changes at best, and monthly is usually adequate for net supply and lake level simulation (this ignores short-term fluctuations associated with storm movement which are not addressed in this study). Likewise, spatial resolution finer than about 1000-5000 km2

 (the present 

average resolution of GLERL's models and their applications) is unnecessary, for use with general 

circulation models (GCMs) of the atmosphere, and much can be done in assessing hydrology 

changes at resolutions of 100,000 - 1,000,000 km2

 with lumped versions of the models. 

The models were assessed partially by computing net basin supplies to the lakes (basin runoff plus 

overlake precipitation minus overlake evaporation) with historical meteorological data for 1951-

80 and comparing to historical net basin supplies. The absolute average annual difference ranged 

from 1.6% to 2.7% on the deep lakes, while the Lake St. Clair and Lake Erie applications were 

12.0% and 7.0% respectively; month-to-month differences showed more variation. These differences generally reflect poorer evaporation modeling on the shallow lakes and snowmelt and 

evapotranspiration model discrepancies for the other lake basins. While monthly differences were 

generally small, a few were significant. The low annual residuals were felt to be acceptable for 

use of these models in assessing changes from the current climate as they would be consistently 

applied to both a "present" and a "changed" climate. Further assessment of model deficiencies 

with comparisons to historical net basin supplies is difficult since the latter are derived from water 

budgets, which incorporate all budget term errors in the derived net basin supplies. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 43

There is some indication of model applicability outside of the time periods over which the models 

were calibrated as indicated above and in Tables 12 and 14. To assess the applicability of the 

process models to a climate warmer than the one under which they were calibrated and verified 

requires access to meteorological data and process outputs for the warmer climate, which unfortunately do not exist. Warm periods early in this century are not sufficiently documented for the 

Great Lakes. In particular, data are lacking on watershed runoff to the lakes, water surface temperatures, wind speed, humidity, cloud cover, and solar insolation. 

It is entirely possible that the models are tied somewhat to the present climate; empiricism is employed in the evapotranspiration component of the LBRM and in some of the heat flux terms in 

the heat balance and lake evaporation model. Coefficients were determined or selected in accordance with the present climate. The models are all based on physical concepts that should be 

good under any climate; however, the assumption is made that they represent processes under a 

changed climate that are the same as the present ones. These include linear reservoir moisture 

storages, partial-area infiltration, lake heat-storage relations with surface temperature, and graybody radiation. However, the calibration and verification periods for the component process 

models include a range of air temperatures, precipitation, and other meteorological variables that 

encompass much of the changes in these variables predicted for a changed climate. Even though 

the changes are transitory in the calibration and verification period data sets, the models appear to 

work well under these conditions. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

 44
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

45

Great Lakes Climate Change Hydrological Responses 

GLERL integrated their hydrological process models into a system to estimate lake levels, wholelake heat storage, and water and energy balances for forecasts and for assessment of impacts associated with climate change (Croley 1990, 1992b; Croley and Hartmann 1987; Croley and Lee

1993). As mentioned earlier, they used this system to simulate the Great Lakes hydrology for historical meteorology and four climate change scenarios generated through GCM experiments 

(CGCM2A, CGCM2B, HADCM3A, and HADCM3B). Behavior is characterized by looking at 

mean annual and seasonal values of each hydrological variable under each of the four climates 

tested, as well as the base case. Selected measures of the variability of each hydrological variable, 

for each of the four climates, also were calculated for the annual periods. These means and measures of variability are compared to those determined with the historical meteorology (which 

serves as a baseline for assessing shifts produced by other regimes). Seasonal steady-state behavior is exemplified here in figures for the Lake Ontario basin and summarized for all lakes and all 

climate-change scenarios for the entire period in annual tables and figures. 

Basin Meteorology 

The annual cycles of all meteorological variables were averaged over the 1950—1999 period and 

inspected; see Table 15 and Figures 15 and 16. The annual air temperatures for the base case increase with decreasing latitude; see Table 15. The overland air temperatures for all four climate 

change scenarios are higher throughout the annual cycle than the base case. The differences are 

greatest for the HADCM3A scenario, followed by the CGCM2A, HADCM3B, and CGCM2B 

scenarios and for the Lakes Michigan and Huron and Georgian Bay; see Table 15. The difference 

is generally smallest during the late spring and early winter and largest during the late winter and 

early fall for all lakes and for all transposed scenarios; as an example, see Figure 16 for the Lake 

Ontario basin. Changes in annual variability of air temperature were remarkably small. Table 16 

shows the average annual steady state standard deviation of air temperature, depicting the variability from year to year in the 50-year period. The annual air temperature variability in Table 16 

appears artificial and is the result of truncation of annual air temperatures to the nearest 0.1oC before the standard deviation was calculated. 

Overland precipitation shows much more variability than air temperature both among scenarios 

and among lake basins. Table 15 and Figure 17 show that generally precipitation is greater on all 

lakes and scenarios, except Michigan and Erie for the CGCM2B scenario and Erie for the 

CGCM2A scenario. The Canadian GCM scenarios generally increase precipitation much less than 

Table 15. Average Annual Basin Meteorology Differences (1950—1999). 

Basin Overland Air Temperature (oC) & 

Climate Scenario Absolute Differencesa

Overland Precipitation (mm) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 2.3 3.0 2.2 3.7 2.7 820 1% 6% 8% 9%

Michigan 7.1 3.6 2.8 3.9 2.9 828 0% -1% 7% 12%

Huron 7.1 3.6 2.8 4.1 3.1 817 2% 1% 7% 14%

Georgian 4.3 3.4 2.4 4.0 3.0 908 3% 3% 11% 13%

St. Clair 8.4 3.5 2.6 4.2 3.1 857 1% 0% 7% 15%

Erie 9.1 3.1 2.4 4.2 3.0 917 -1% -4% 6% 16%

Ontario 7.2 3.2 2.2 4.0 3.0 941 5% 1% 9% 13% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

46

do the Hadley GCM scenarios. The largest 

increase occurs on Georgian Bay for the 

HADCM3A scenario and on Erie for the HADCM3B scenario. 

The CGCM2B scenario seasonal precipitation variability is similar to the base case for Lake Ontario, see Figure 16 for the Ontario basin. The CGCM2A scenario shows more variability seasonally but the HADCM3B scenario shows the most variability with both spring and late summer 

peaks for Ontario. On the Lake Superior basin, all scenarios are very similar to the base case with 

only slightly higher spring precipitation for the HADCM3A and HADCM3B scenarios and slightly 

higher early summer precipitation for the HADCM3A, HADCM3B, and CGCM2A scenarios. 

There is also slightly higher fall precipitation for the CGCM2B scenario on Superior. On Michigan, we see a little more variability among the different scenarios throughout the season than with 

Superior, with the HADCM3B showing higher spring precipitation. Huron is similar to Michigan 

Figure 15. Daily Average Air Temperature 

Averaged Over The Year. 

-10

30

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

0

120

0

110

0

90

Overland Air Temperature ( °C)

Overland Precipitation (mm)

Evapotranspiration (mm)

Overland Runoff (mm)

J FMAMJ J ASOND

Figure 16. Seasonal Lake Ontario Basin Average Meteorology and Hydrology. 

Table 16. Average Annual Basin Meteorology Standard Deviation Differences (1950—1999). 

Basin Overland Air Temperature Std. Dev. (oC) & 

Climate Scenario Relative Changea

Overland Precipitation Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 0.9 0% 0% 0% 0% 81.6 3% 6% 7% 9%

Michigan 0.7 0% 0% 0% 0% 84.7 3% -1% 7% 11%

Huron 0.7 0% 0% 0% 0% 84.8 4% 2% 6% 15%

Georgian 0.8 0% -1% 0% 0% 87.9 5% 4% 11% 13%

St. Clair 0.7 -1% 0% 0% 0% 119.8 3% 0% 5% 14%

Erie 0.7 0% 0% 1% 0% 109.8 2% -3% 6% 16%

Ontario 0.7 0% 0% 0% 0% 88.5 9% 2% 7% 10% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

47

with the HADCM3B scenario showing higher 

spring precipitation but also slightly higher 

summer precipitation also. All scenarios except CGCM2A show higher winter precipitation on Georgian Bay with only slightly higher 

values through the rest of the year. St. Clair 

and Erie show higher precipitation for all scenarios except CGCM2A, with the HADCM3B 

peaking highest in spring and fall. 

Changes in annual variability of precipitation 

are also more pronounced than for air temperature; see Table 16. Generally, the Hadley scenarios, which are the wettest in Table 15, also 

are the more variable as seen in Table 16. This 

is expected since if precipitation is generally 

closer to its lower bound of zero, its variation 

must therefore be diminished too. 

Basin Hydrology 

The increased air temperatures, consequent in 

all of the changed climates, significantly alter 

the heat balance of the surface. As seen in Table 17, the snow pack is drastically reduced as the 

relative change varies among scenarios and lake basins from a 26% to an 84% drop in accumulated snow moisture. Furthermore, evapotranspiration increases significantly by 8% to 27%. Neither snow moisture reductions nor evapotranspiration increases mirror temperature changes perfectly for the four scenarios; see Figures 18 and 19. The snow pack is reduced the most under 

scenario CGCM2A and next most under scenario HADCM3A in Table 17 and Figure 18 while 

Table 15 reveals that scenario HADCM3A is warmer overall than CGCM2A and both are warmer 

than the remaining scenarios. The remaining scenarios in order of warmest are HADCM3B and 

CGCM2B; this order appears also for snow pack reductions in Table 17 only for Lakes Superior, 

St. Clair, Erie, and Ontario, but is reversed for Lakes Michigan and Huron and Georgian Bay. 

This lack of perfect correspondence between snow pack reductions and air temperature increases 

is due to the pattern of precipitation changes. Thus, while the HADCM3A scenario is warmer 

than the CGCM2A scenario, it is also much wetter; this allows higher snow pack reduction under 

the CGCM2A scenario. Likewise, evapotranspiration is highest for the two Hadley GCM scenarios in Table 17 and Figure 19 since they are the wettest, even though the CGCM2A scenario is 

warmer than the HADCM3B scenario. After all, evapotranspiration is limited by water supply, 

which is higher under the two Hadley GCM scenarios. The increased evapotranspiration and decreased snow pack give rise to less moisture available in the soil and groundwater zones. Table 

17 and Figures 20 and 21 show a general lowering of soil moisture that is most acute for the 

CGCM2A scenario and a corresponding loss of groundwater storage in the same pattern. By 

adding snow water equivalent, soil moisture, groundwater, and surface storage (not shown in Table 17), the total moisture storage is computed as in Table 17 and shown in Figure 22. The pattern is the same there; the CGCM2A scenario shows the most acute loss of moisture storage in 

the basin, but all scenarios show a general loss as compared to the base case. The next highest 

Figure 17. Average Annual Total Precipitation.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

48

loss of moisture storage occurs for the HADCM3A scenario. Note that the anomalously high 

groundwater (and consequently total moisture storage) for Georgian Bay in Table 17 results from 

unrealistic initial groundwater conditions in the models consistent with earlier calibrations and are 

arbitrary. They are omitted in Figures 21 and 22. On other basins, estimated groundwater is 

much faster, compared to the Georgian Bay calibrations, and initial conditions are unimportant. 

The net effect of the increased air temperatures, through increased evapotranspiration and decreased moisture storage in the basins, is decreased runoff; see Table 17 and Figure 23. While 

Table 17 and Figure 23 do indeed show decreased runoff in many cases, there are other cases 

where runoff increases since moisture reductions are offset by precipitation increases. Table 17 

and Figure 23 generally show the greatest runoff decreases for the scenarios in the following order: CGCM2A, CGCM2B, HADCM3A, and HADCM3B. 

Table 17. Average Annual Basin Hydrology Differences (1950—1999). 

Basin Snow Water Equivalent (mm) & 

Climate Scenario Relative Changesa

Soil Moisture (mm) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 50.9 -40% -26% -39% -28% 41.9 -15% -8% -16% -7%

Michigan 11.8 -79% -65% -66% -57% 34.9 -21% -15% -17% -5%

Huron 13.6 -84% -70% -73% -67% 29.0 -18% -13% -12% 0%

Georgian 37.6 -73% -53% -57% -48% 70.7 -10% -7% -8% -1%

St. Clair 7.9 -83% -67% -75% -70% 6.0 -34% -26% -26% -12%

Erie 5.5 -76% -58% -75% -67% 6.8 -30% -25% -29% -15%

Ontario 15.1 -75% -58% -73% -67% 21.0 -13% -9% -10% -1%

Basin Groundwater (mm) & 

Climate Scenario Relative Changesa

Total Basin Moisture (mm) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 149 -15% -9% -13% -7% 300 -19% -11% -18% -10%

Michigan 62 -19% -14% -14% -3% 116 -26% -20% -20% -9%

Huron 104 -16% -12% -14% -2% 151 -23% -18% -19% -8%

Georgian 26894 -1% 0% 0% 0% 27014 -1% -1% 0% 0%

St. Clair 10 -23% -19% -14% 2% 27 -43% -34% -34% -22%

Erie 8 -24% -19% -14% 2% 24 -38% -31% -32% -18%

Ontario 11 -15% -10% -8% 3% 61 -28% -21% -25% -16%

Basin Overland Evapotranspiration (mm) & 

Climate Scenario Relative Changesa

Runoff as an Overland Depth (mm) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 425 17% 17% 27% 21% 397 -15% -6% -11% -4%

Michigan 506 13% 9% 20% 20% 324 -20% -16% -13% -1%

Huron 502 18% 13% 21% 22% 464 -22% -16% -14% 1%

Georgian 482 17% 13% 26% 22% 420 -12% -7% -5% 2%

St. Clair 544 17% 11% 20% 22% 315 -26% -20% -14% 3%

Erie 572 12% 8% 18% 22% 347 -22% -22% -13% 7%

Ontario 476 23% 12% 26% 23% 466 -13% -10% -8% 2% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

49

Figure 20. Daily Soil Moisture Storage 

Averaged Over The Year. 

Figure 21. Groundwater Storage Averaged 

Over The Year. 

Figure 18. Daily Snow Water Equivalent 

Averaged Over The Year. Figure 19. Average Annual Evapotranspiration.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

50

Figure 22. Daily Total Moisture Storage 

Averaged Over The Year. 

Figure 23. Average Annual Total Basin Runoff.

Figure 16 depicts typical seasonal behavior for evapotranspiration and runoff on the Ontario basin. On the Superior and Michigan basins, there are early summer evapotranspiration peaks, 

compared to the base case. Huron and Georgian Bay have evapotranspiration peaks extending 

over the summer and fall and evapotranspiration is still larger than the base case throughout the 

rest of the year. St. Clair and Erie have evapotranspiration generally with the same seasonal cycle 

as the base case but with higher values 

throughout the year. Ontario evapotranspiration (Figure 16) is also generally higher 

throughout the year with a similar seasonal 

cycle as the base case, except for the 

HADCM3B scenario, which has peaks in the 

late summer. All basins show slightly earlier 

spring snow melt and earlier but lower runoff 

peaks, except for the HADCM3B scenario, as 

shown for Ontario in Figure 16. Georgian Bay 

includes the HADCM3B scenario; spring runoff is lower for all changed climates than the 

base case. 

Figure 24 shows typical seasonal behavior for 

basin moisture storage quantities depicted in 

Figures 20—23. As expected from inspection 

of seasonal runoff in Figure 16 and discussed 

0

50

0

20

0

130

0

70

Snow Water Equivalent (mm)

Soil Storage (mm)

Groundwater Storage (mm)

Total Moisture Storage (mm)

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

J FMAMJ J ASOND

Figure 24. Seasonal Lake Ontario Basin Average Moisture Storage. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

51

previously, the snow pack in Figure 24 is much reduced from the base case under all climate 

change scenarios. The CGCM2A scenario gives the most snow pack reduction for all lake basins, 

as seen in Figure 24 for the Lake Ontario basin. Soil moisture storages for all climate change scenarios are correspondingly higher than the base case during the winter months and lower during 

the rest of the year on all basins, as depicted in Figure 24 for the Lake Ontario basin, except for 

the Lake St. Clair and Erie basins. There, soil moisture storage for all climate change scenarios 

are lower than the base case throughout the entire season. Groundwater moisture storages for all 

climate change scenarios are lower than the base case throughout the entire season on all basins 

but with the same seasonal pattern as the base case, as depicted in Figure 24 for the Lake Ontario 

basin, except for the Lake St. Clair and Erie basins. There, the Hadley climate change scenarios 

show slightly higher groundwater moisture storage than the base case during the winter months 

only. Total moisture storages in all but one Great Lake basin are similar to that shown in Figure 

24 for the Lake Ontario basin. On the Superior, Michigan, Huron, St. Clair, Erie, and Ontario 

basins, total moisture storage for all changed climate scenarios lies generally below the base case. 

The CGCM2A scenario has the lowest total moisture storage (most reduction from the base case) 

during the spring and summer and the HADCM3A has the lowest during the fall and winter. The 

HADCM3B scenario has the highest total moisture storage (least reduction from the base case) all 

year round. The Lake Ontario basin has the most winter/spring reductions of total moisture storage of all the lakes, for all climate change scenarios. On the Georgian Bay basin, total moisture 

storage lies beneath the base case for the CGCM2A, CGCM2B, and HADCM3A scenarios. The 

CGCM2A scenario has the lowest total moisture storage all year long and the HADCM3B has the 

highest, almost identical to the base case. 

Table 18 shows expected changes in variability for basin moisture storage variables. Snow water 

variability is greatly decreased simply because snow water is greatly decreased toward its lower 

bound of zero. Relative annual changes in variability of soil moisture, groundwater, surface storage (not shown), and total basin moisture are small (less than half when ignoring anomalous 

Georgian Bay groundwater and total moisture storage due to antecedent groundwater conditions 

on a few subbasins already discussed). Table 18 also shows evapotranspiration with more variability, generally, for the Hadley GCM scenarios. This corresponds the greatest and most variable 

precipitation; see Tables 15 and 16, respectively. This results from the fact that evapotranspiration is a moisture-limited process; only the amount in storage can evaporate or transpire and 

where there is more variability in the moisture supply will there be more variability in the 

evapotranspiration amounts. There generally is not much change in basin runoff variability in Table 18, although the Canadian GCM scenarios do show reduction while the extreme HADCM3B 

scenario shows a slight increase in variability due to the increased variability of its annual precipitation. 

Over Water Meteorology 

The over water air temperature, humidity, and wind speed differ from over land since the lower 

atmospheric layer is affected by the water surface over which it lies. The model corrections to 

over-land meteorological observations for over-water conditions depend heavily on the water surface temperature, which in turn is a function of the over-water meteorology and heat balance at 

the surface of the lake. Table 19 and Figures 25—28 summarize annual average steady-state 

over-water meteorology differences. In general, the synergistic relationship that exists between 

air and water temperature in a changed climate yields a general increase in both that follows the 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

52

base climate patterns, similar to over-land behavior. Table 19 and Figure 25 show that over water 

air temperatures for all climate scenarios are higher than the base case. The differences are greatest for the HADCM3A scenario, followed by the CGCM2A, HADCM3B, and CGCM2B scenarios and for Lakes Michigan and Huron and Georgian Bay. 

While the smallest overland air temperature annual changes occurred for Lake Superior in all climate change scenarios (see Table 15), the smallest over water air temperatures occur on Lakes St. 

Clair and Erie because of their very low heat storage capacity. Likewise, by comparing Tables 15 

and 19, we see that the over-water air temperature increase is larger than the overland air temperature increase for deeper Lakes Superior, Michigan, and Ontario, and is smaller for shallower 

Lakes St. Clair and Erie. Over-water absolute humidity is increased for all scenarios; see Table 19 

and Figure 26 and is greatest for the CGCM2A scenario although it is very similar for all scenarios. Both over water air temperature and overlake humidity show an increase and a slight shift 

earlier in the seasonal cycle, for all lakes and all scenarios; this is typified in Figure 29 for Lake 

Table 18. Average Annual Basin Hydrology Standard Deviation Differences (1950—1999). 

Basin Snow Water Equivalent Std. Dev. (mm) & 

Climate Scenario Relative Changea

Soil Moisture Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 13.2 -9% 1% -12% -1% 5.2 -15% -9% -15% -9%

Michigan 5.4 -70% -50% -54% -45% 5.4 -16% -13% -14% -4%

Huron 6.9 -78% -58% -65% -58% 4.3 -16% -12% -9% 2%

Georgian 12.0 -52% -22% -33% -24% 8.9 -6% -4% 1% 4%

St. Clair 5.5 -77% -56% -64% -58% 1.2 -17% -14% -13% -4%

Erie 3.5 -62% -43% -61% -48% 1.1 -20% -21% -21% -11%

Ontario 9.6 -65% -44% -68% -63% 2.4 -11% -9% -5% 0%

Basin Groundwater Std. Dev. (mm) & 

Climate Scenario Relative Changea

Total Moisture Storage Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 11.8 -13% -12% -15% -15% 25.0 -11% -5% -12% -10%

Michigan 6.1 -18% -16% -15% -5% 13.6 -26% -20% -19% -9%

Huron 5.9 -12% -6% -3% 5% 11.0 -26% -20% -15% -7%

Georgian 110.6 -68% -55% -41% 4% 113.6 -67% -54% -39% 5%

St. Clair 1.9 -15% -13% -5% 7% 7.1 -49% -35% -38% -30%

Erie 1.3 -17% -12% -2% 10% 4.9 -40% -31% -36% -24%

Ontario 1.4 -11% -9% 1% 8% 10.6 -41% -29% -42% -37%

Basin Overland Evapotranspira. Std. Dev. (mm) &

Climate Scenario Relative Changea

Runoff as Overland Depth Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 39.2 23% 21% 34% 25% 38.2 -3% 3% 1% 6%

Michigan 46.6 19% 11% 25% 21% 41.0 -15% -13% -6% 5%

Huron 47.0 23% 15% 26% 26% 69.8 -16% -12% -8% 6%

Georgian 44.8 21% 15% 26% 22% 44.2 -10% -6% 0% 7%

St. Clair 66.7 18% 13% 20% 20% 69.0 -14% -11% -5% 10%

Erie 59.4 15% 10% 18% 20% 65.2 -11% -14% -3% 15%

Ontario 42.0 29% 15% 31% 24% 55.9 -5% -6% 0% 8% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

53

Ontario. The shift reflects interaction of the atmosphere with the lake’s heat storage, which is 

discussed subsequently. This pattern is reflected in water surface temperatures as well, also discussed subsequently. 

Cloud cover, shown in Table 19 and Figure 27, is reduced for the Hadley climate change scenarios; this might not be expected since those scenarios were wetter (more precipitation) than the 

Canadian climate change scenarios. Also absolute humidity was a little higher than base case for 

all scenarios and all lakes. Seasonally, the behavior is consistent across most of the Great Lakes. 

Figure 29, while for Lake Ontario, shows the variation in cloud cover that is typical of all lakes 

except Erie and St. Clair. Generally, all climate change scenarios are slightly higher than the base 

case during the winter and beginning of spring, as shown in Figure 29. During the late spring, all 

scenarios are lower than the base case. The CGCM2A and CGCM2B scenarios are then higher 

and the HADCM3A and HADCM3B scenarios are lower than the base case in the summer and 

fall. On Lakes Erie and St. Clair, the seasonal cycle is very similar except that during the late 

summer, cloud cover for all scenarios is less than the base case. 

Overlake wind speed, shown in Table 19 and Figure 28, increases over the base case on all Great 

Lakes for both of the Canadian climate change scenarios and for the HADCM3B scenario. The 

HADCM3A scenario is slightly above or slightly below the base case, depending on the lake. The 

Canadian climate change scenarios show more difference with the base case than do the Hadley 

scenarios. This might be due to additional atmospheric instability associated with slightly drier 

conditions in the Canadian climate change scenarios. Figure 29 typifies the other Great Lakes; 

average wind speeds for all climate change scenarios slightly exceed those for the base case in the 

winter and are very close to the base case throughout the rest of the year. 

Table 19. Average Annual Overlake Meteorology Differences (1950—1999). 

Basin Air Temperature (oC) & 

Climate Scenario Absolute Differencesa

Humidity (mb) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 3.4 3.7 2.6 4.0 3.3 7.0 2.5 1.8 2.2 2.1

Michigan 7.4 4.2 3.1 4.2 3.4 9.3 3.1 2.2 2.4 2.3

Huron 6.8 3.9 2.8 4.0 3.3 8.8 2.8 2.0 2.2 2.0

Georgian 5.9 4.0 2.7 4.1 3.3 8.4 2.8 1.9 2.1 1.9

St. Clair 10.0 3.2 2.3 3.9 3.1 10.7 2.9 2.1 2.1 2.1

Erie 9.8 3.2 2.3 3.9 3.1 10.7 2.9 2.1 2.3 2.1

Ontario 8.1 3.7 2.6 4.0 3.2 9.5 3.0 2.1 2.2 2.0

Basin Cloud Cover (%) & 

Climate Scenario Relative Changesa

Wind Speed (m s-1) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 56.7 4% 3% -5% -3% 5.3 5% 5% 1% 1%

Michigan 60.7 5% 2% -5% -1% 5.9 6% 5% -1% 1%

Huron 57.3 7% 5% -4% -1% 5.6 6% 5% 0% 1%

Georgian 58.8 7% 5% -4% -2% 5.6 7% 6% 1% 2%

St. Clair 57.6 1% 0% -4% 1% 5.3 4% 4% -1% 1%

Erie 61.4 2% 1% -3% 1% 6.0 5% 4% -2% 0%

Ontario 58.1 5% 4% -4% -1% 5.8 4% 4% -2% 0% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

54

Variability in overlake meteorology is shown for annual values in Table 20. Overlake air temperature variability is generally reduced on all lakes for all scenarios. The deeper lakes (Michigan, 

Huron, Georgian Bay, and Ontario), with more heat storage capacity than shallow Lake St. Clair 

or Lake Erie, have the greatest reduction in variability. Monomictic lakes (where surface temperature never drops below that of maximum water density, failing to induce buoyancy-driven 

Figure 25. Daily Surface Air Temperature Averaged Over The Year. 

Figure 27. Daily Cloud Cover Averaged Over 

The Year. 

Figure 26. Daily Absolute Humidity Averaged 

Over The Year. 

Figure 28. Daily Average Wind Speed Averaged Over The Year. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

55

turnover of the water column) have a rather 

difficult-to-penetrate lower bound on their 

temperature, which would reduce their variability, while dimictic lakes (where buoyancydriven turnovers occur), which often have ice, 

are less constrained. Lakes St. Clair and Erie 

remain dimictic under the changed climates 

while the other lakes become largely monomictic. Lake Superior variance drops only a little 

relative to the other deep lakes even though it 

is deepest. Superior becomes monomictic less 

often than the other deep lakes; it is northern 

most with lower temperatures (see Table 19). 

Therefore, variability reduction is limited over 

Lake Superior. Humidity variability increases 

generally for all climate change scenarios; the 

largest is associated with the HADCM3A scenario; see Table 20. Cloud cover variability is 

slightly reduced with the most reduction under 

the Hadley scenarios. Wind speed variability 

changes little in the Hadley but increases for all 

lakes in the Canadian scenarios; see Table 20. 

0

25

0

10

0

100

-10

30

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

J FMAMJ J ASOND

Overlake Air Temperature (°C)

Absolute Humidity (mb)

Wind Speed (m/s)

Cloud Cover (%)

Figure 29. Seasonal Lake Ontario Average 

Overlake Meteorology. 

Table 20. Average Annual Overlake Meteorology Standard Deviation Differences (1950—1999). 

Basin Air Temperature Std. Dev. (oC) & 

Climate Scenario Relative Changea

Humidity Std. Dev. (mb) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 1.0 -5% 0% -2% -5% 0.6 8% 13% 24% 5%

Michigan 0.9 -18% -9% -11% -12% 0.6 -7% -2% 6% -5%

Huron 0.8 -11% -6% -8% -10% 0.5 1% 2% 14% -1%

Georgian 1.0 -8% -5% -5% -7% 0.6 5% 6% 17% 2%

St. Clair 0.8 -4% -3% -2% -3% 0.5 4% 3% 16% 3%

Erie 0.9 -7% -5% -4% -6% 0.5 3% 3% 16% 3%

Ontario 0.9 -21% -12% -16% -17% 0.6 -7% -4% 4% -7%

Basin Cloud Cover Std. Dev. (%) & 

Climate Scenario Relative Changea Wind Speed Std. Dev. (m s-1) & Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 2.5 0% 0% -2% -1% 0.4 10% 8% 3% 3%

Michigan 3.1 -1% -1% -3% -2% 0.2 16% 12% 1% 5%

Huron 4.8 -2% -1% -4% -3% 0.2 11% 10% -1% 1%

Georgian 3.9 -3% -2% -5% -4% 0.3 15% 11% 3% 4%

St. Clair 2.8 -1% 0% -5% -4% 0.3 4% 4% -4% -2%

Erie 2.9 0% 0% -3% -2% 0.2 5% 6% -4% -1%

Ontario 3.2 -1% -1% -4% -3% 0.3 8% 8% 1% 2% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

56

Lake Heat Balance 

Annual lake heat balance changes are depicted in Table 21 and a seasonal example for Lake Ontario is given in Figure 30. Insolation changes in Table 21 reflect largely the cloud cover changes 

given earlier in Table 19; the Hadley GCM changed-climate scenarios transfer more heat into the 

lakes than do the Canadian GCM scenarios. The increase for the Hadley GCM climate-change 

scenarios occurs on all Great Lakes beginning in the late spring, extending throughout the summer, and into the early fall; Figure 30 is typical. Insolation for the Hadley GCM climate-change 

scenarios then is slightly below the base case beginning in the late fall, extending throughout the 

winter and into the early spring. The insolation for the Canadian GCM climate-change scenarios 

is slightly less than the base case throughout the year for all lakes; the decrease is spread throughout the annual cycle fairly uniformly and the seasonal insolation variation is similar to the base 

case. Again, Figure 30 is typical of the other lakes. Reflection generally decreases but changes 

are very small, relative to the insolation changes, with most of the difference coming in the winterspring due to the absence of ice cover. Table 21 shows that the Canadian GCM climate-change 

Table 21. Average Annual Lake Heat Flux Differences (1950—1999). 

Basin Insolation (W m-2) & 

Climate Scenario Absolute Differencesa

Reflection (W m-2) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 158 -4 -2 7 5 -18 2 2 1 2

Michigan 148 -4 -2 7 3 -15 1 1 0 0

Huron 160 -6 -4 8 4 -17 2 1 0 1

Georgian 159 -6 -5 8 5 -23 7 6 6 6

St. Clair 155 -1 -1 7 2 -28 5 4 5 5

Erie 150 -2 -1 7 2 -20 4 3 3 4

Ontario 149 -4 -3 7 3 -15 1 1 0 0

Basin Net Long Wave Exchange (W m-2) & 

Climate Scenario Absolute Differencesa

Latent Heat Flux (W m-2) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior -61 10 7 4 4 -45 -8 -6 -13 -9

Michigan -58 11 8 5 5 -51 -10 -9 -15 -11

Huron -65 11 8 4 5 -51 -9 -6 -15 -11

Georgian -64 12 9 5 5 -49 -11 -8 -18 -14

St. Clair -55 10 7 7 8 -65 -13 -10 -19 -14

Erie -42 12 8 7 8 -70 -12 -9 -18 -13

Ontario -58 10 8 5 5 -53 -8 -5 -14 -10

Basin Sensible Heat Flux (W m-2) & 

Climate Scenario Absolute Differencesa

Net Heat Flux (W m-2) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior -34 0 -1 1 -1 0 0 0 0 0

Michigan -23 3 3 4 2 -1 -1 0 -1 -1

Huron -27 2 1 2 1 -1 0 0 -1 0

Georgian -22 -2 -2 -1 -2 -1 0 0 -1 0

St. Clair -5 -1 0 2 0 -2 -1 -1 -1 -1

Erie -16 -2 -1 2 0 -2 -1 -1 -1 -1

Ontario -23 2 1 4 3 -1 0 0 -1 0 a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

57

scenarios reduce reflection more than the Hadley scenarios (reflection is negative coming out 

of the lake surface). Figure 30, for Lake Ontario, does not show this behavior partly because reflection is plotted at the same scale 

used in the other plots in Figure 30, which 

hides its relative seasonal variation, and partly 

because Lake Ontario ice cover, which was 

already small compared to the other lakes in 

the base case, is reduced less by the changedclimate scenarios. Thus, Lake Ontario has less 

reflection changes during the winter-spring due 

to absence of ice cover than other Great Lakes 

under all climate-change scenarios. 

Net long wave exchange increases slightly, implying more heat stays in the lakes. Table 21 

shows that the largest increase on all lakes occurs under the CGCM2A scenario followed by 

the CGCM2B, HADCM3B, and HADCM3A 

scenarios respectively. Increases are spread 

fairly uniformly throughout the seasonal cycle 

as typified in Figure 30 for Lake Ontario, although this is difficult to see because of the 

scale used. Sensible heat exchange changes are small and vary in direction from lake to lake; see 

Table 21. The overall increases in heat storage in the lakes thus far discussed are balanced by increases in evaporation, shown in Table 21 as a significant decrease in latent heat transferred into 

the lake. These evaporation increases are rather large compared to the base case. The seasonal 

patterns of net long wave exchange, sensible heat transfer, and latent heat transfer are very similar 

to the base case; see Figure 30. The changes shown in these variables, summarized in Table 21, 

are distributed fairly uniformly throughout the seasonal cycle; again Figure 30 is fairly typical of 

the pattern of changes observed on all lakes although it is difficult to see in some cases (for relatively small components like reflection) because of the scale used. The annual total heat flux 

should remain close to zero for all scenarios, as in the base case, indicating that there is no longterm heat storage in the lakes and energy conservation is satisfied. Table 21 shows this and Figure 30 indicates that the change in the seasonal variation of total heat flux is very similar to the 

base case; increased heat fluxes are balanced largely by evaporation. 

Changes in variability in lake heat balance variables are summarized in Table 22. As seen there, 

insolation is less variable than in the base case, reflecting the decreased cloud cover variability 

shown in Table 20. In particular, trends in cloud cover are reflected directly in solar insolation; on 

any lake, the reduced variability under all scenarios of insolation in Table 22 matches the reduced 

variability of cloud cover in Table 20. The reduced variability of Lake Ontario insolation in Table 

22 matches the reduced variability of cloud cover in Table 20. 

-30

0

-100

0

-120

0

-90

10

-240

200

270

0

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

J FMAMJ J ASOND

Insolation (watts/m ) 2

Reflection

Net Long Wave

Latent

Sensible

Total (Net) Flux

(watts/m ) 2

(watts/m ) 2

(watts/m ) 2

(watts/m ) 2

(watts/m ) 2

Figure 30. Seasonal Lake Ontario Average 

Lake Heat Fluxes. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

58

The variability of reflection in Table 22 is generally greatly reduced, except on Lake St. Clair, reflecting the greatly reduced ice cover under the transposed climates. Without ice cover, reflection 

is from the water surface only and the fraction of incoming radiation reflected remains more 

nearly constant throughout the seasonal cycle. Lake St. Clair has the smallest relative change in 

ice cover under all scenarios of all the Great Lakes, which have ice cover practically eliminated. 

Sensible heat transfer is seen in Table 22 to be more variable only on Superior and Michigan for 

the Canadian GCM climate-change scenarios and on Lake St. Clair for all scenarios; sensible heat 

transfer variability is greatly increased on Lake St. Clair. Again, the absence of any real heat storage on Lake St. Clair precludes the filtering effect possible with such storages on meteorology 

and heat transfers. Also, given little heat capacity, the anomaly in reflection results in an anomaly 

in sensible heat flux on Lake St. Clair. Latent heat transfer is seen in Table 22 to be only slightly 

less variable than the base case for the Canadian GCM climate-change scenarios on all lakes except Michigan and for the Hadley scenarios on only Georgian Bay, and Lakes St. Clair and Erie. 

Table 22. Average Annual Lake Heat Flux Standard Deviation Differences (1950-1999). 

Basin Insolation Std. Dev. (W m-2) & 

Climate Scenario Relative Changea

Reflection Std. Dev. (W m-2) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 4.5 0% 0% -1% -1% 2.5 -82% -82% -82% -82%

Michigan 5.1 -1% -1% -3% -2% 1.3 -60% -60% -61% -61%

Huron 7.5 -1% -1% -3% -2% 2.2 -66% -66% -67% -67%

Georgian 6.8 -2% -2% -3% -2% 3.5 -79% -58% -73% -69%

St. Clair 4.6 -1% -1% -4% -3% 1.7 11% -7% 20% 13%

Erie 4.7 0% 0% -2% -2% 3.0 -56% -27% -49% -47%

Ontario 5.0 0% -1% -3% -2% 0.8 -38% -38% -39% -39%

Basin Net Long Wave Exchange Std. Dev. (W m-2) &

Climate Scenario Relative Changea

Latent Heat Flux Std. Dev. (W m-2) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 3.0 3% 2% 10% 2% 4.9 -4% -7% 2% -6%

Michigan 2.8 7% 4% 11% 5% 5.2 1% 1% 4% 0%

Huron 3.2 1% 1% 4% 2% 5.5 -1% -3% 2% -3%

Georgian 2.6 -2% -1% 2% 0% 6.1 -9% -8% -6% -9%

St. Clair 2.6 -3% -1% 1% -5% 4.4 -1% -1% -1% -2%

Erie 2.8 0% 0% 4% -1% 5.6 -11% -5% -6% -9%

Ontario 2.3 0% 0% 6% 1% 4.7 -3% -2% 3% 1%

Basin Sensible Heat Flux Std. Dev. (W m-2) & 

Climate Scenario Relative Changea

Net Heat Flux Std. Dev. (W m-2) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 5.2 1% 2% -2% -2% 0.1 22% 22% 42% 29%

Michigan 3.4 3% 4% 0% 0% 0.1 2% 7% 16% 7%

Huron 4.1 -11% -10% -14% -13% 0.1 29% 18% 39% 26%

Georgian 4.0 -18% -17% -20% -19% 0.2 25% 15% 34% 24%

St. Clair 0.9 19% 10% 19% 17% 0.2 -1% 0% 4% 0%

Erie 2.6 -4% -1% -11% -8% 0.2 8% 5% 15% 6%

Ontario 3.2 -1% 0% -4% -3% 0.1 11% 5% 21% 10% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

59

The net effect of variability changes in all of the heat balance components for a lake is an increase 

in variability in the total flux as shown in Table 22. 

The heat budget gives rise to increased water surface temperatures as seen in Table 23 and Figure 

31. Stored heat increases 19% to 42% over the Great Lakes, depending on the changed-climate 

scenario considered; see Table 23. The largest relative heat increases are seen to occur for the 

northeastern-most lakes and for the CGCM2A, HADCM3A, HADCM3B, and CGCM2B 

changed-climates scenarios, in decreasing order of impact on all lakes. The stored heat appears as 

a constant amount higher throughout the seasonal cycle, since we are looking at steady-state conditions; see Figure 32 for the average Lake Ontario seasonal cycle. The increased heat in storage 

also means that ice formation will be greatly reduced over winter on the deep Great Lakes. Ice 

cover is practically eliminated under all transposed climate scenarios on all lakes but Lake St. 

Clair, and to a lesser extent on Lake Erie; since those lakes have very little heat storage capacity, 

ice formation is not affected as much as elsewhere; see Table 23. 

Table 23 also shows that the average steady-state increase in water surface temperatures for all 

changed-climate scenarios on all lakes range from 2.1oC on Lake St. Clair (CGCM2B scenario) to 

4.2oC on Lake Michigan (CGCM2A scenario). The heat storage capacity of a lake influences the 

increase in water surface temperatures that can almost be seen in Figure 32. Water surface temperatures are seen to peak slightly earlier on deep lakes under the transposed climates than under 

the base case. The increased heat in storage is sufficient to cause increased lake evaporation on 

all lakes under all scenarios, even though wind speeds and humidity, by themselves, would not 

increase evaporation. (Wind speed and humidity changes, in some cases, would decrease lake 

evaporation, all other things being equal.) Table 23 shows increases in annual lake evaporation of 

Table 23. Average Annual Lake Heat Balance Differences (1950—1999). 

Basin Stored Heat (1017 cal) & 

Climate Scenario Relative Changesa

Ice Cover (%) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 48.3 36% 24% 36% 32% 4.1 -100% -100% -100% -100%

Michigan 23.2 41% 28% 35% 31% 1.4 -100% -100% -100% -100%

Huron 16.5 42% 28% 40% 34% 2.3 -100% -100% -100% -100%

Georgian 4.8 42% 26% 41% 34% 14.3 -99% -87% -96% -94%

St. Clair 0.0 33% 25% 36% 33% 35.8 -31% -21% -33% -31%

Erie 4.9 26% 19% 28% 23% 13.9 -86% -53% -80% -77%

Ontario 8.8 40% 24% 35% 29% 0.7 -100% -98% -100% -100%

Basin Water Surface Temperature (oC) & 

Climate Scenario Absolute Differencesa

Lake Evaporation Depth (mm) & 

Climate Scenario Relative Changesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 5.8 3.7 2.5 3.9 3.4 575 18% 14% 29% 21%

Michigan 8.3 4.2 3.0 4.1 3.5 651 21% 17% 30% 22%

Huron 8.4 3.7 2.5 3.8 3.2 654 17% 12% 29% 21%

Georgian 7.8 3.4 2.2 3.6 2.9 628 23% 17% 36% 29%

St. Clair 10.6 2.9 2.1 3.2 2.6 835 20% 16% 30% 23%

Erie 11.0 3.0 2.1 3.3 2.7 898 18% 13% 27% 19%

Ontario 9.1 3.8 2.6 3.9 3.3 674 16% 10% 27% 20% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

60

evaporation of 10% to 36%, depending on the 

lake and the scenario. The most evaporation occurs on all lakes for the HADCM3A scenario, followed in order by the HADCM3B, CGCM2A, and CGCM2B scenarios. See also Figure 33. 

The variabilities associated with the lake heat balance variables are summarized in Table 24. The 

stored heat exhibits some increase in variability, in Table 24, for all scenarios and all lakes except 

Lake St. Clair for the Hadley GCM climate-change scenarios. Also, since the ice pack is not present anymore, the variability associated with 

the ice pack is zero (ice pack stays at a constant zero value). This means a relative 

change of 100% in the standard deviation of 

ice cover in Table 24. The increased heat 

storage in the Lakes Michigan, Huron, and 

Ontario (see Table 23) results in a greater 

thermal inertia for these lakes and the water 

surface temperature is less variable; see Table 

24. Finally, the variability of lake evaporation 

ranges from little change to reductions across 

the Great Lakes and across the various 

changed-climate scenarios. 

Lake Thermal Structure 

The deep lakes (Superior, Michigan, Huron, 

Georgian Bay, and Ontario) have water surface temperatures that stay above 3.98oC 

throughout the annual cycle in some years for Figure 33. Average Annual Evaporation. 

Figure 31. Daily Surface Water Temperature 

Averaged Over The Year. 

0

18 Stored Heat (10 cal) 18

0

5 Ice Cover (%)

0

30 Water Temperature (°C)

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

J FMAMJ J ASOND

Figure 32. Seasonal Lake Ontario Average 

Lake Heat Storage Characteristics. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

61

some of the changed-climate scenarios (less often on Superior since it is so far north). Figure 32 

partly illustrates this for Lake Ontario for all of the changed-climate scenarios. This means that 

buoyancy-driven turnovers of the water column do not occur in the same way as they do at present. In some years, the large lakes are changed from dimictic lakes (turnovers occur twice a year 

as water temperatures pass through the point of maximum density, 3.98oC) to monomictic lakes 

(maximum turnover occurs at the temperature “reversal” where temperatures stop declining and 

start rising again and the minimum temperature is greater than 3.98oC). 

Lake Water Balance 

Overlake precipitation, runoff, and lake evaporation, all expressed as depths over each lake surface, sum algebraically as the net basin supply to the lake and are presented in Table 25. Annual 

summaries on all lakes for evaporation, precipitation, runoff, and net basin supply are shown in 

Figures 33, 34, 35, and 36, respectively. Overlake precipitation in Table 25 is not identical with 

over land precipitation in Table 15; they were both estimated via Thiessen weighting over different areas. The observations, presented previously, on overland precipitation equally apply for 

overlake precipitation; recall lake effects are ignored for precipitation. Table 25 and Figure 34 

show that generally precipitation is greater on all lakes and scenarios, except Michigan, St. Clair, 

and Erie for the Canadian GCM climate-change scenarios. The Canadian GCM scenarios generally increase precipitation much less than do the Hadley GCM scenarios. The largest increases 

again occur on Georgian Bay for the HADCM3A scenario and on Erie for the HADCM3B scenario (see Tables 25 and 15). 

Basin runoff in Table 25 is expressed as an over water depth and will appear different than values 

in Table 18 where it is expressed as an over land depth. While Table 25 and Figure 35 do indeed 

Table 24. Average Annual Lake Heat Balance Standard Deviation Differences (1950—1999). 

Basin Stored Heat Std. Dev. (1017 cal) & 

Climate Scenario Relative Changea

Ice Cover Std. Dev. (%) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 4.0 35% 33% 38% 25% 5.3 -100% -100% -100% -100%

Michigan 2.1 21% 7% 12% 2% 2.6 -100% -100% -100% -100%

Huron 1.5 26% 15% 25% 14% 4.8 -100% -100% -100% -100%

Georgian 0.5 15% 13% 17% 10% 7.8 -92% -56% -79% -71%

St. Clair 0.0 3% 12% -25% -5% 3.7 38% 1% 50% 48%

Erie 0.3 10% 2% 17% 10% 8.1 -54% -17% -44% -38%

Ontario 0.8 50% 20% 47% 29% 1.6 -100% -95% -100% -100%

Basin Water Surface Temperature Std. Dev. (oC) & 

Climate Scenario Relative Changea

Lake Evaporation Depth Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 0.9 5% 16% 13% 7% 61.9 -4% -7% 2% -6%

Michigan 1.0 -25% -9% -12% -15% 66.9 0% 1% 3% -1%

Huron 0.9 -13% -3% -7% -10% 69.7 -1% -3% 3% -2%

Georgian 1.0 4% 6% 9% 4% 78.9 -9% -9% -7% -9%

St. Clair 0.7 1% -2% 9% 5% 58.3 -2% -2% -2% -2%

Erie 0.8 5% 1% 12% 6% 72.9 -12% -5% -7% -10%

Ontario 1.0 -29% -15% -20% -22% 60.3 -4% -2% 3% 0% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

62

Table 25. Average Annual Lake Water Balance Differences (1950—1999). 

Basin Overlake Precipitation (mm) & 

Climate Scenario Absolute Differencesa

Runoff as Overwater Depth (mm) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 796 16 59 73 67 620 -94 -35 -70 -27

Michigan 821 -5 -12 49 89 648 -133 -106 -85 -8

Huron 833 25 10 73 112 393 -86 -65 -53 3

Georgian 913 33 7 103 120 1811 -209 -135 -89 28

St. Clair 813 -13 -39 46 127 4445 -1142 -901 -641 142

Erie 923 -12 -29 82 162 818 -179 -181 -108 57

Ontario 878 52 15 75 111 1722 -219 -169 -144 42

Basin Lake Evaporation Depth (mm) & 

Climate Scenario Absolute Differencesa

Net Basin Supply (mm) & 

Climate Scenario Absolute Differencesa

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 575 103 78 165 119 841 -180 -54 -161 -80

Michigan 651 135 113 196 141 818 -273 -232 -232 -59

Huron 654 112 80 187 136 572 -173 -135 -168 -21

Georgian 628 147 105 229 180 2096 -323 -232 -215 -33

St. Clair 835 170 133 251 188 4423 -1325 -1073 -847 81

Erie 898 159 119 239 173 843 -350 -330 -266 45

Ontario 674 105 69 185 132 1926 -272 -223 -254 21 a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.

show decreased runoff in many cases, there are other cases where runoff increases since moisture 

reductions are offset by precipitation increases. Table 25 and Figure 35 generally show the greatest runoff decreases for the scenarios in the following order: CGCM2A, CGCM2B, HADCM3A, 

and HADCM3B, as was true for runoff expressed as an overland depth in Table 18 and Figure 23. 

Figure 34. Average Annual Precipitation. Figure 35. Average Annual Lake Runoff. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

63

Evaporation in Table 25, however, does agree 

with Table 23 since it is expressed as an over 

water depth in both places. Lake evaporation 

is simply repeated from Table 23 for convenience. Also, precipitation, runoff, and evaporation are presented as absolute differences 

from the base case, rather than relative 

changes. Net basin supply in Table 25 and 

Figure 36 is generally less than the base case 

for all changed-climate scenarios on all lakes 

except for HADCM3B scenario on St. Clair, 

Erie, and Ontario. The greatest reductions in 

net basin supply occur on all lakes under the 

CGCM2A scenario, followed by either the 

CGCM2B or HADCM3A scenarios depending 

on the lake; the smallest reductions occur on 

all lakes under the HADCM3B scenario. 

A seasonal summary for Lake Ontario is given 

in Figure 37. Observations on seasonal variability in over water precipitation mirror those made 

for over land precipitation in Figure 16. The CGCM2B scenario seasonal precipitation variability 

is similar to the base case for Lake Ontario. The CGCM2A scenario shows more variability seasonally but the HADCM3B scenario shows the most variability with both spring and late summer 

peaks for Ontario. On the Lake Superior basin, all scenarios are very similar to the base case with 

only slightly higher spring precipitation for the HADCM3A and HADCM3B scenarios and slightly 

higher early summer precipitation for the HADCM3A, HADCM3B, and CGCM2A scenarios. 

There is also slightly higher fall precipitation 

for the CGCM2B scenario on Superior. On 

Michigan, we see a little more variability 

among the different scenarios throughout the 

season than with Superior, with the 

HADCM3B showing higher spring precipitation. Huron is similar to Michigan with the 

HADCM3B scenario showing higher spring 

precipitation and slightly higher summer precipitation. All scenarios except CGCM2A 

show higher winter precipitation on Georgian 

Bay with only slightly higher values through 

the rest of the year. St. Clair and Erie show 

higher precipitation for all scenarios except 

CGCM2A, with the HADCM3B peaking in 

spring and fall. Likewise, observations on seasonal variability in runoff are similar to those 

made earlier in Figure 16. All basins show earlier but lower runoff peaks, except for the 

Figure 36. Average Annual Net Basin Supply.

0

300

0

110

0

120

-10

360

Overlake Runoff (mm)

Precipitation (mm)

Evaporation (mm)

Net Basin Supply (mm)

CGCM2A

CGCM2B

HadCM3A

HadCM3B

Base

J FMAMJ J ASOND

Figure 37. Seasonal Lake Ontario Average Net 

Basin Supply Components. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

64

HADCM3B scenario, as shown for Ontario in Figure 37. The exception is Georgian Bay; there, 

spring runoff is lower for all changed climates than the base case, including the HADCM3B scenario. Observations on lake evaporation were already made (for latent heat flux) in Figure 30. 

Figure 37 illustrates that most of the seasonal variability in net basin supply comes from the runoff 

and to a lesser extent from the evaporation while the variability among the climate-change scenarios in net basin supply comes from the runoff. The seasonal variability for net basin supply is similar to the base case for all changed-climate scenarios and lakes, as exemplified in Figure 37 for 

Lake Ontario. Lake Superior has all changed-climate scenario net basin supplies below the base 

case for the late spring through the fall; for the winter to the late spring, each changed-climate 

scenario is greater than the base for just one month, but otherwise lower. Lakes Michigan and 

Huron are similar to Superior except that the HADCM3B scenario exceeds the base case net basin supply for December and February-April. Michigan net basin supply under the CGCM2B scenario also exceeds the base case for February-March. Georgian Bay net basin supply, under all 

changed-climate scenarios, is below the base for mid-spring through mid-fall and above for the 

springtime. St. Clair and Erie net basin supply, under all changed-climate scenarios, are below the 

base for mid-spring through the summer; the HADCM3B scenario rises above the base during 

mid-fall through early spring. As seen in Figure 37, Lake Ontario net basin supply for both Hadley GCM changed-climate scenarios is above the base case during the late fall through the winter 

and below during the spring to late fall. The Canadian GCM changed-climate scenarios have net 

basin supply generally below the base case except for the late summer and early winter. 

The variabilities associated with the net basin supplies and its components are summarized in Table 26 for all lakes and scenarios. Changes in annual variability of over lake precipitation in Table 

26 are similar to those for over land precipitation in Table 16. Generally, the Hadley scenarios, 

Table 26. Average Annual Lake Water Balance Standard Deviation Differences (1950—1999). 

Basin Overlake Precipitation Std. Dev. (mm) & 

Climate Scenario Relative Changea

Runoff as Overwater Depth Std. Dev. (mm) &

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 95 2% 8% 8% 9% 60 -3% 3% 1% 6%

Michigan 90 1% -1% 6% 9% 82 -15% -13% -6% 5%

Huron 82 4% 2% 9% 15% 59 -16% -12% -8% 6%

Georgian 94 5% 2% 12% 15% 191 -10% -6% 0% 7%

St. Clair 135 0% -5% 3% 13% 975 -14% -11% -5% 10%

Erie 119 -1% -2% 8% 16% 154 -11% -14% -3% 15%

Ontario 91 11% 3% 6% 10% 206 -5% -6% 0% 8%

Basin Lake Evaporation Depth Std. Dev. (mm) & 

Climate Scenario Relative Changea

Net Basin Supply Std. Dev. (mm) & 

Climate Scenario Relative Changea

 BASE #1 #2 #3 #4 BASE #1 #2 #3 #4

Superior 61.9 -4% -7% 2% -6% 162 -5% -1% 1% 2%

Michigan 66.9 0% 1% 3% -1% 192 -5% -5% 0% 4%

Huron 69.7 -1% -3% 3% -2% 158 -3% -3% 0% 7%

Georgian 78.9 -9% -9% -7% -9% 289 -5% -5% 2% 8%

St. Clair 58.3 -2% -2% -2% -2% 1102 -12% -11% -4% 10%

Erie 72.9 -12% -5% -7% -10% 285 -9% -10% -1% 11%

Ontario 60.3 -4% -2% 3% 0% 305 -3% -4% -1% 6% a

Scenario #1 is CGCM2A; #2 is CGCM2B; #3 is HADCM3A; #4 is HADCM3B.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

65

which are the wettest in Table 25, also are the more variable as seen in Table 26. This is expected 

since if precipitation is generally closer to its lower bound of zero, its variation must therefore be 

diminished too. There generally is not much change in basin runoff variability in Table 26, although the Canadian GCM scenarios do show reduction while the extreme HADCM3B scenario 

shows a slight increase in variability due to the increased variability of its annual precipitation. 

This is as observed, of course, in Table 18 and the results (relative changes in standard deviation) 

are identical. Finally, the variability of lake evaporation ranges from little change to reductions 

across the Great Lakes and across the various changed-climate scenarios, as shown in Tables 24 

and 26. 

Table 27 summarizes the changes in the hydrological and net basin supply components for the entire Great Lakes basin; they were computed by converting the equivalent depths of Table 26 to 

annual flow rates on each lake and adding them over all the lakes. The changes from the base 

case are also expressed relatively in Table 27. Also expressed relatively are changes from other 

studies that used other GCMs (Croley 1990, 1993a; Lofgren et al. 2002; Croley and Luukkonen

2003), or transposed climates (Croley et al. 1998; Kunkel et al. 1998); they are provided for 

comparison. Net basin supplies to the Great Lakes taken as a whole are seen to drop to about 

one sixth to one quarter under both Canadian GCM changed-climate scenarios and the first Hadley scenario (CGCM2A, CGCM2B, and HADCM3A). This drop in net basin supply seems to 

result from the increases in overlake evaporation and overland evapotranspiration (reducing subsequent runoff to the lakes). While evaporation and evapotranspiration have increased just as significantly under the second Hadley GCM changed-climate scenario (HADCM3B) as well, the precipitation increases (both overland and overlake) compensate and the net basin supplies are very 

close to the base case. The results from the Canadian GCM changed-climate scenarios then, are 

similar to the earlier studies with the previous Canadian GCMs, also reported in Table 27; the net 

supplies drop in the same range due to increased basin evapotranspiration and lake evaporation. 

The results from the Hadley GCM changed-climate scenarios however, are not similar to the earlier studies with the previous Hadley GCMS, also reported in Table 27; the newer runs show a 

drop in net basin supply while the older ones showed an increase. Table 27 also shows that the 

present results are contained within (bounded by) results of the earlier climate transposition study 

and are not as severe as the early IJC or 1989 EPA studies. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

66

Table 27. Average Annual Great Lakes Basin Hydrology Summary. 

Scenario Overland Evapo- Basin Overlake Overlake Net Basin 

 Precipitation transpiration Runoff Precipitation Evaporation Supply 

 (m3 s

-1) (m3

 s

-1) (m3

 s

-1) (m3

 s

-1) (m3

 s

-1) (m3

 s

-1) 

Basea 14,300 8,060 6,240 6,480 5,050 7,660

CGCM2Ab 14,520 2% 9,370 16% 5,200 -17% 6,590 2% 6,000 19% 5,790 -24%

CGCM2Bc 14,500 1% 9,030 12% 5,510 -12% 6,610 2% 5,770 14% 6,350 -17%

HADCM3Ad 15,450 8% 9,920 23% 5,580 -11% 7,030 8% 6,530 29% 6,080 -21%

HADCM3Be 16,070 12% 9,790 21% 6,250 0% 7,230 12% 6,130 21% 7,350 -4%

CGCM1 2030f -10% 2% 15% -16%

CGCM1 2050g -14% 3% 22% -23%

CGCM1 2090h -20% 12% 34% -29%

HADCM2 2030i 1% 7% 6% 2%

HADCM2 2050j 3% 7% 11% 1%

HADCM2 2090k 7% 19% 17% 10%

6oS × 10oWl 6% 31% -25% 3% 49% -48%

6oS × 0oWm 24% 43% -1% 25% 33% -1%

10oS × 11oWn 17% 48% -21% 13% 75% -54%

10oS × 5oWo 45% 78% 2% 45% 69% -5%

CCCp -2% 22% -32% 0% 32% -46%

GISSq 2% 21% -24% 4% 27% -37%

GFDLr 1% 19% -23% 0% 44% -51%

OSUs 6% 19% -11% 6% 26% -23% a

Historical (1950-1999) period simulation. 

b

Canadian Centre for Climate Modeling and Analysis, GCM 2, run A21 (warm and dry). 

c

Canadian Centre for Climate Modeling and Analysis, GCM 2, run B23 (not as warm but dry). 

d

 Hadley Centre for Climate Prediction and Research, GCM 3, run A1FI (warm and wet). 

e

 Hadley Centre for Climate Prediction and Research, GCM 3, run B22 (not as warm but wet). 

f

Canadian Centre for Climate Modeling and Analysis, GCM 1, run 2021—2040 (Lofgren et al. 2002). 

g

Canadian Centre for Climate Modeling and Analysis, GCM 1, run 2041—2060 (Lofgren et al. 2002). 

h

Canadian Centre for Climate Modeling and Analysis, GCM 1, run 2081—2100 (Lofgren et al. 2002). 

i

Hadley Centre for Climate Prediction and Research, GCM 2, run 2021—2040 (Lofgren et al. 2002). 

j

Hadley Centre for Climate Prediction and Research, GCM 2, run 2040—2060 (Lofgren et al. 2002). 

k

Hadley Centre for Climate Prediction and Research, GCM 2, run 2081—2100 (Lofgren et al. 2002). 

l

Climate transferred from 6oS and 10oW of Great Lakes (Croley et al. 1998). mClimate transferred from 6oS of Great Lakes (Croley et al. 1998). n

Climate transferred from 10oS and 11oW of Great Lakes (Croley et al. 1998). o

Climate transferred from 10oS and 5oW of Great Lakes (Croley et al. 1998). 

p

Canadian Climate Centre (Croley 1993a); IJC study. 

q

Goddard Institute for Space Studies GCM (Croley 1990); 1989 EPA study. r

Geophysical Fluid Dynamics Laboratory GCM (Croley 1990); 1989 EPA study. s

Oregon State University GCM (Croley 1990); 1989 EPA study.
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

67

Hydrological Sensitivities 

Main Findings 

Without temperatures below freezing, the snow pack is insensitive to precipitation. Although the 

changed-climate scenarios on different lakes show different estimates of precipitation change, 

each shows increases in air temperatures that significantly reduce the snow pack. Thus, even if 

precipitation increases more than suggested by these scenarios, the snow pack will be much reduced under warmer climates. The increased air temperatures significantly increase evapotranspiration. Neither snow moisture reductions nor evapotranspiration increases mirror temperature 

changes perfectly for the four scenarios; this lack of perfect correspondence is due to the pattern 

of precipitation changes. The increased evapotranspiration and decreased snow pack give rise to 

less moisture available in the soil and groundwater zones, and consequently decreased runoff. 

While there is decreased runoff in many cases, there are other cases where runoff increases since 

moisture reductions are offset by precipitation increases. Runoff decreases, from largest to smallest, for scenarios in order: CGCM2A, CGCM2B, HADCM3A, and HADCM3B. 

Insolation changes reflect largely the cloud cover changes; the Hadley GCM changed-climate scenarios transfer more heat into the lakes than do the Canadian GCM scenarios. The increase for 

the Hadley GCM changed-climate scenarios occurs on all Great Lakes beginning in the late 

spring, extending throughout the summer, and into the early fall. Insolation for the Hadley GCM 

changed-climate scenarios then is slightly below the base case beginning in the late fall, extending 

throughout the winter and into the early spring. The insolation for the Canadian GCM climatechange scenarios is slightly less than the base case throughout the year for all lakes; the decrease 

is spread throughout the annual cycle fairly uniformly and the seasonal insolation variation is similar to the base case. Reflection generally decreases but changes are very small, relative to the insolation changes, with most of the difference coming in the winter-spring due to the absence of 

ice cover. The Canadian GCM climate-change scenarios reduce reflection more than the Hadley 

scenarios. Net long wave exchange increases slightly, implying more heat stays in the lakes. The 

largest increase on all lakes occurs under the CGCM2A scenario followed by the CGCM2B, 

HADCM3B, and HADCM3A scenarios respectively. Increases are spread fairly uniformly 

throughout the seasonal cycle. Sensible heat exchange changes are small and vary in direction 

from lake to lake. 

The heat budget gives rise to increased water surface temperatures and stored heat increases over 

the Great Lakes, depending on the changed-climate scenario considered. The largest relative heat 

increases are seen to occur for the northeastern-most lakes and for the CGCM2A, HADCM3A, 

HADCM3B, and CGCM2B changed-climates scenarios, in decreasing order of impact on all 

lakes. The increased heat in storage also means that ice formation will be greatly reduced over 

winter on the deep Great Lakes. Ice cover is practically eliminated under all changed climate scenarios on all lakes but Lake St. Clair, and to a lesser extent on Lake Erie; since those lakes have 

very little heat storage capacity, ice formation is not affected as much as elsewhere. 

Water surface temperatures are seen to peak slightly earlier on deep lakes under the changed climates than under the base case. The increased heat in storage is sufficient to cause increased lake 

evaporation on all lakes under all scenarios, even though wind speeds and humidity, by themselves, 

would not increase evaporation. (Wind speed and humidity changes, in some cases, would de-
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

68

crease lake evaporation, all other things being equal.) The most evaporation occurs on all lakes for 

the HADCM3A scenario, followed in order by HADCM3B, CGCM2A, and CGCM2B. 

The deep lakes have water surface temperatures that stay above 3.98oC throughout the annual 

cycle in some years for some of the changed-climate scenarios. This means that buoyancy-driven 

turnovers of the water column do not occur in the same way as they do at present. In some years, 

the large lakes are changed from dimictic lakes to monomictic lakes. Without biannual turnovers, 

hypolimnion chemistry may be altered; oxygen may be depleted, releasing nutrients and metals 

from lake sediments. The lakes may experience more than a single winter turnover if temperature 

gradients are small and winds are strong enough to induce mixing (Hutchinson 1957). 

The Hadley scenarios generally increase precipitation more than do the Canadian GCM scenarios. 

Precipitation is greater than the base case on all lakes for the Hadley scenarios. For the Canadian 

scenarios, precipitation is greater on all lakes except Michigan, St. Clair, and Erie. The largest 

occur on Georgian Bay for the HADCM3A scenario and on Erie for HADCM3B. 

Net basin supply is generally less than the base case for all changed-climate scenarios for all lakes 

except for the HADCM3B scenario on Lakes St. Clair, Erie, and Ontario. The greatest reductions in net basin supply occur on all lakes under the CGCM2A (warm, dry) scenario, followed by 

either the CGCM2B (less warm, dry) or HADCM3A (warm, wet) scenarios depending on the 

lake; the smallest reductions occur on all lakes under the HADCM3B (less warm, wet) scenario. 

Summary 

The higher air temperatures under the changed-climate scenarios lead to higher over-land 

evapotranspiration and lower runoff to the lakes with earlier runoff peaks since snow pack is reduced and the snow season is greatly reduced. This also results in a reduction in available soil 

moisture. Water temperatures increase and peak earlier; heat resident in the deep lakes increases 

throughout the year. Mixing of the water column diminishes, as most of the lakes become mostly 

monomictic, and lake evaporation increases. Ice formation is greatly reduced over winter on the 

deep Great Lakes, and lake evaporation increases; average net supplies drop most where precipitation increases are modest. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

69

References 

Allsopp, T. R., and S. J. Cohen, 1986. CO2-Induced climate change and its potential impact on 

the Province of Ontario. In: Preprint Volume, Conference on Climate and Water Management 

- A Critical Era, American Meteorological Society, Boston, Massachusetts, 285-290. 

Assel, R. A., 1983. A computerized data base of ice concentration for the Great Lakes. NOAA 

Data Report ERL GLERL-24, Great Lakes Environmental Research Laboratory, Ann Arbor, 

Michigan. 

Assel, R. A., F. H. Quinn, G. A. Leshkevich, and S. J. Bolsenga, 1983. NOAA Great Lakes Ice 

Atlas. Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan. 

Barrow, E., 2002. Climate change in the Great Lakes—St. Lawrence region, a comparison of climate change scenarios. Report prepared for the International Joint Commission’s Lake Ontario—St. Lawrence River Study. 

Bates, G. T., S. W. Hostetler, and F. Giorgi, 1995. Two-year simulation of the Great Lakes Region with a coupled modeling system. Monthly Weather Review, 123:1505-1522. 

Blumberg A. F., and D. M. DiToro, 1989. The effects of climate warming on Lake Erie water 

quality. In The Potential Effects of Global Climate Change on the United States, J. B. Smith 

and D. A. Tirpak (Eds.), U. S. Environmental Protection Agency report no. EPA-230-05-89-

051, 7-1 - 7-28. 

Bolsenga S. J., 1977. Lake-land precipitation relationships using Northern Lake Michigan data. 

Journal of Applied Meteorology, 16(11):1158-1164. 

Bolsenga S. J., 1979. Determining overwater precipitation from overland data: the methodological 

controversy analyzed. Journal of Great Lakes Research, 5(3-4):301-311. 

Bolsenga, S. J., and J. C. Hagman, 1975. On the selection of representative stations for Thiessen 

polygon networks to estimate Lake Ontario overwater precipitation. International Field Year 

for the Great Lakes Bulletin 16, National Oceanic and Atmospheric Administration, Rockville, 

57-62. 

Campbell J. E., A. H. Clites, and G. M. Green, 1987. Measurements of ice motion in Lake Erie 

using satellite-tracked drifter buoys. NOAA Data Report ERL GLERL-30, Great Lakes Environmental Research Laboratory, Ann Arbor, Michigan. 

Charlson, R. J., S. E. Schwartz, J. M. Hales, R. D. Cess, J. A. Coakley, Jr., J. E. Hansen, and D. J. 

Hofmann, 1992: Climate forcing by anthropogenic aerosols. Science, 255, 423-430. 

Cohen, S. J., 1986. Impacts of CO2-induced climatic change on water resources in the Great 

Lakes basin. Climatic Change, 8:135-153. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

70

Cohen, S. J., 1990a. Methodological issues in regional impacts research. In: Proceedings of an 

International Symposium/Workshop on Climate Change, Implications for Water and Ecological Resources, G. Wall and M. Sanderson (Eds.), Department of Geography Publication Series, Occasional Paper No. 11, University of Waterloo, Waterloo, Ontario, 31-43. 

Cohen, S. J., 1991. Caveats in applying GCM output to regional impact assessments. Proceedings of A Symposium on Climate Scenarios, The Water Network, University of Waterloo, Waterloo, 16-32. 

Coordinating Committee on Great Lakes Basic Hydraulic and Hydrologic Data, 1977. Coordinated Great Lakes Physical Data. U. S. Army District Engineer, Detroit. 

Croley, T. E., II, 1982. Great Lakes basins runoff modeling. NOAA Technical Memorandum ERL 

GLERL-39, National Technical Information Servicer, Springfield. 

Croley, T. E., II, 1983a. Great Lakes basins (U.S.A.-Canada) runoff modeling. Journal of Hydrology, 64:135-158. 

Croley, T. E., II, 1983b. Lake Ontario basin (U.S.A.-Canada) runoff modeling. Journal of Hydrology, 66:101-121. 

Croley, T. E., II, 1989a. Lumped modeling of Laurentian Great Lakes evaporation, heat storage, 

and energy fluxes for forecasting and simulation. NOAA Technical Memorandum ERL 

GLERL-70, Great Lakes Environmental Research Laboratory, Ann Arbor. 

Croley, T. E., II, 1989b. Verifiable evaporation modeling on the Laurentian Great Lakes. Water 

Resource Research, 25(5):781-792. 

Croley, T. E., II, 1990. Laurentian Great Lakes double-CO2 climate change hydrological impacts. 

Climatic Change, 17:27-47. 

Croley, T. E., II, 1992a. Long-term heat storage in the Great Lakes. Water Resources Research, 

28(1):69-81. 

Croley, T. E., II, 1992b. Climate change impacts on Great Lakes water supplies. Proceedings of 

the Symposium on Managing Water Resources During Global Change, Twenty-Eighth American Water Resources Association Conference, 241-250. 

Croley, T. E., II, 1993a. CCC GCM 2xCO2 hydrological impacts on the Great Lakes. In: Climate, 

Climate Change, Water Level Forecasting and Frequency Analysis, Supporting Documents, 

Volume 1 - Water Supply Scenarios, International Joint Commission, Washington, D. C. 

Croley, T. E., II, 1993b. Probabilistic Great Lakes hydrology outlooks. Water Resources Bulletin, 29(5):741-753. 

Croley, T. E., II, and R. A. Assel, 1994. A one-dimensional ice thermodynamics model for the 

Laurentian Great Lakes. Water Resources Research, 30(3):625-639. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

71

Croley, T. E., II, and H. C. Hartmann, 1984. Lake Superior basin runoff modeling. NOAA Technical Memorandum ERL GLERL-50, National Technical Information Service, Springfield. 

Croley, T. E., II, and H. C. Hartmann, 1985. Resolving Thiessen polygons. Journal of Hydrology, 76:363-379. 

Croley, T. E., II, and H. C. Hartmann, 1986. Near-real-time gorecasting of large-lake water supplies; a user's manual. NOAA Technical Memorandum ERL GLERL-61, Environmental Research Laboratories, Boulder, Colorado. 

Croley, T. E., II, and H. C. Hartmann, 1987. Near-real-time forecasting of large lake supplies. 

Journal of the Water Resources Planning and Management Division, 113(6):810-823. 

Croley, T. E., II, and H. C. Hartmann, 1989. Effects of climate changes on the Laurentian Great 

Lakes levels. In The Potential Effects of Global Climate Change on the United States: Appendix A-Water Resources J. B. Smith and D. A. Tirpak (Eds.), U.S. Environmental Protection 

Agency, Washington, D.C., 4-1 - 4-34. 

Croley, T. E., II, and D. H. Lee, 1993. Evaluation of Great Lakes net basin supply forecasts. Water Resources Bulletin, 29(2):267-282. 

Croley, T. E., II, and C. L. Luukkonen, 2003. Potential climate change impacts on Lansing, Michigan ground water. Journal of the American Water Resources Association, 39(1): 149-163. 

Croley, T. E., II, F. H. Quinn, K. E., Kunkel, and S. J. Changnon, 1998. Great Lakes hydrology 

under transposed climates, Climatic Change, 38:405-433. 

DeCooke, B. G., and D. F. Witherspoon, 1981. Terrestrial water balance. In IFYGL - The International Field Year for the Great Lakes, E. J. Aubert and T. L. Richards (Eds.), Great Lakes 

Environmental Research Laboratory, Ann Arbor, 210-219. 

Freeman, N. G., and W. S. Haras, 1978. What you always wanted to know about Great Lakes 

levels and didn't know whom to ask. Environment Canada, Ottawa. 

Gauthier, R. L., R. A. Melloh, T. E. Croley II, and H. C. Hartmann, 1984. In Proceedings 18th 

International Symposium on Remote Sensing of the Environment, Paris, 1-12. 

Gray, D. M., G. A. McKay, and J. M. Wigham, 1973. Energy, evaporation, and evapotranspiration. In Handbook on the Principles of Hydrology, DM Gray (Ed.), Water Information Center, New York, 3.1-3.66. 

Green, G. M., and S. I. Outcalt, 1985. A simulation model of river ice cover thermodynamics. 

Cold Reg. Sci. & Technol., 10:251-262. 

Hartmann, H. C., 1987. An evaluation of Great Lakes hydraulic routing models. NOAA Technical 

Memorandum ERL GLERL-66, Great Lakes Environmental Research Laboratory, Ann Arbor. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

72

Hartmann, H. C., 1988. Historical basis for limit on Lake Superior water level regulations. Journal of Great Lakes Research, 14(3):316-324. 

Hartmann, H. C., 1990. Climate change impacts on Laurentian Great Lakes levels. Climatic 

Change, 17:49-67. 

Hostetler, S. W., and P. J. Bartlein, 1990. Simulation of lake evaporation with application to 

modeling lake level variations of Harney-Malheur Lake, Oregon. Wat. Resour. Res., 

26(10):2603-2612. 

Hutchinson, G. E., 1957. A Treatise on Limnology, Volume 1, Part 1 - Geography and Physics of 

Lakes, John Wiley and Sons, New York. 

Intergovernmental Panel on Climate Change, 2000. Special Report on Emissions Scenarios. N. 

Nakicenovic and R. Swart (Eds.), Cambridge University Press, Cambridge, United Kingdom 

and New York. 

International Great Lakes Diversions and Consumptives Uses Study Board, 1981. Great Lakes 

Diversions and Consumptive Uses. International Joint Commission, Washington, D. C. 

International Great Lakes Diversions and Consumptives Uses Study Board, 1985. Great Lakes 

Diversions and Consumptive Uses. International Joint Commission, Washington, D. C. 

International Lake Superior Board of Control, 1981. Regulation of Lake Superior: Plan 1977 

Development, Description, and Testing. International Joint Commission, Washington, D. C. 

International Lake Superior Board of Control, 1982. Regulation of Lake Superior: Operational 

Guides for Plan 1977. International Joint Commission, Washington, D. C. 

International St. Lawrence River Board of Control, 1963. Regulation of Lake Ontario: Plan 

1958-D. International Joint Commission, Washington, D. C. 

Keijman, J. Q., 1974. The estimation of the energy balance of a lake from simple weather data. 

Boundary-Layer Meteorology, 7:399-407. 

Kraus, E. B., and J. S. Turner, 1967. A one-dimensional model of the seasonal thermocline II; the 

general theory and its consequences. Tellus, 19:98-105. 

Kunkel, K. E., S. J. Changnon, T. E. Croley II, and F. H. Quinn, 1998. Transposed climates for 

study of water supply variability on the Laurentian Great Lakes, Climatic Change, 38:387-404. 

Larsen, C. E., 1985. A stratigraphic study of beach features on the southwestern shore of Lake 

Michigan: new evidence of holocene lake level fluctuations. Environmental Geology Notes 

112, Illinois State Geological Survey, Champaign. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

73

Lofgren, B. M, F. H. Quinn, A. H. Clites, R. A. Assel, A. J. Eberhardt, and C. L. Luukkonen, 

2002. Evaluation of potential impacts on Great Lakes water resources based on climate scenarios of two GCMs. J. Great Lakes Res., 28(4):537-554. 

Louie, P. Y. T., 1991. Proposed GCM scenarios for the phase 2 study. Proceedings of A Symposium on Climate Scenarios, The Water Network, University of Waterloo, Waterloo, 67-78. 

Manabe, S., and R. T. Wetherald, 1975. The effects of doubling the CO2 concentration on the 

climate of a general circulation model. J. Atmos. Sci., 32:3-15. 

McCormick, M. J., 1989. Potential climate changes to the Lake Michigan thermal structure. In 

The Potential Effects of Global Climate Change on the United States, J. B. Smith and D. A. 

Tirpak (Eds.), U. S. Environmental Protection Agency report no. EPA-230-05-89-051, 6-1 - 

6-26. 

McCormick, M. J. and G. A. Meadows, 1988. An intercomparison of four mixed layer models in a 

shallow inland sea. J. Geophys. Res., 93(C6):6774-6788. 

McFarlane, N. A., 1991. The Canadian Climate Centre second-generation global circulation 

model. Proceedings of A Symposium on Climate Scenarios, The Water Network, University 

of Waterloo, Waterloo, 3-15. 

Phillips, W. D., and J. G. Irbe, 1978. Land-to-lake comparison of wind, temperature, and humidity 

on Lake Ontario during the International Field Year for the Great Lakes (IFYGL). Report 

CLI-2-77, Environment Canada, Atmospheric Environment Service, Downsview. 

Quinn, F. H., 1978. Hydrologic response model of the North American Great Lakes. Journal of 

Hydrology, 37:295-307. 

Quinn, F. H., 1979. An improved aerodynamic evaporation technique for large lakes with application to the International Field Year for the Great Lakes. Water Resources Research, 

15(4):935-940. 

Quinn, F. H., 1981. Secular changes in annual and seasonal Great Lakes precipitation, 1854-1979, 

and their implications for Great Lakes water resource studies. Water Resources Research, 

17:1619-1624. 

Quinn, F. H., 1982. Trends and extremes of Lake Erie water supplies. Proceedings International 

Symposium on Hydrometeorology, American Water Resources Association, Minneapolis, 267-

270. 

Quinn, F. H., 1985. Great Lakes water levels. In Great Lakes Water Levels, Briefing of Senators 

and Representatives from the Great Lakes Basin July 19, International Joint Commission, 

Washington, 1-24. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

74

Quinn, F. H., 1988. Likely effects of climate changes on water levels in the Great Lakes. In: Proceedings, First North American Conference on Preparing for Climate Change, Climate 

Change Institute, Washington, D. C., 481-487. 

Quinn, F. H., and T. E. Croley II, 1981. The role of precipitation climatology in hydrologic design 

and planning on the Laurentian Great Lakes. Proceedings Fourth Conference on Hydrometeorology, American Meteorological Society, Boston, 218-223. 

Quinn, F. H., and T. E. Croley II, 1983. Climatic water balance models for Great Lakes forecasting and simulation. In: Preprint Volume: Fifth Conference on Hydrometeorology, American 

Meteorological Society, Boston, Massachusetts, 218-223. 

Quinn, F. H., and R. N. Kelley, 1983. Great Lakes monthly hydrologic data. NOAA Technical 

Memorandum ERL GLERL-39, National Technical Information Service, Springfield. 

Quinn, F. H., and D. C. Norton, 1982. Great Lakes precipitation by months, 1900-80. NOAA 

Technical Memorandum ERL GLERL-20, National Technical Information Service, Springfield. 

Quinn, F. H., T. E. Croley II, K. Kunkel, and S. J. Changnon, 1997. Laurentian Great Lakes hydrology and lake levels under the transposed 1993 Mississippi River flood climate. Journal of 

Great Lakes Research, 23(3):317-327. 

Robinson, P. J. and P. Finkelstein, 1989. Strategies for the Development of Climate Scenarios for 

Impact Assessment. U. S. Environmental Protection Agency, Research Triangle Park, North 

Carolina. 

Rondy, D. R., 1976. Great Lakes ice cover, Appendix 4, Great Lakes Basin Framework Study, 

Great Lakes Basin Commission, Ann Arbor. 

U. S. Army Corps of Engineers, 1985. Great Lakes water level facts. U. S. Government Printing 

Office, Washington, D. C. 

U. S. Environmental Protection Agency, 1984. Potential Climatic Impacts of Increasing Atmospheric CO2 with Emphasis on Water Availability and Hydrology in the United States, EPA Office of Policy, Planning, and Evaluation, Washington, D. C. 

U. S. Environmental Protection Agency, 1989. The Potential Effects of Global Climate Change 

on the United States. Report to Congress. J. B. Smith and D. A. Tirpak (Eds.), Report EPA230-05-89-050, EPA Office of Policy, Planning, and Evaluation, Washington, D. C. 

Wilson, J. W., 1977. Effect of Lake Ontario on precipitation. Monthly Weather Review, 105:207-

214. 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

75

Appendix - Notation 

a = wind parameter, T > 3.98°C [evaporation model empirical parameter]

a' = wind parameter, T < 3.98°C [evaporation model empirical parameter]

as = proportionality constant for snowmelt per degree-day [runoff model empirical parameter]

A = area of the ice surface 

Ab = area of the watershed 

Aw = area of the open-water (ice-free) lake surface 

αdp = deep percolation coefficient [runoff model empirical parameter]

αgw = groundwater coefficient [runoff model empirical parameter]

αint = interflow coefficient [runoff model empirical parameter]

αper = percolation coefficient [runoff model empirical parameter]

αsf = surface outflow coefficient [runoff model empirical parameter]

b = wind parameter, T > 3.98°C [evaporation model empirical parameter]

b' = wind parameter, T < 3.98°C [evaporation model empirical parameter]

b1 = empirical constant 

b2 = empirical constant 

β = partial linear reservoir coefficient 

βeg = groundwater zone evapotranspiration coefficient [runoff model empirical parameter] (= 0) 

βel = lower zone evapotranspiration coefficient [runoff model empirical parameter] (= 0) 

βes = surface zone evapotranspiration coefficient [runoff model empirical parameter]

βeu = upper zone evapotranspiration coefficient [runoff model empirical parameter]

Ci = specific heat of ice 

Cp = specific heat of air at constant temperature 

Cw = specific heat of water 

CE = bulk evaporation coefficient over water 

CE' = bulk evaporation coefficient over ice 

CH = sensible heat coefficient over water 

CH' = sensible heat coefficient over ice 

D = ice pack depth (thickness) 

DD = degree-days per day 

∆ = time increment of mass balance computation period 

e = evaporation or evapotranspiration rate 

ep = rate of evaporation or evapotranspiration still possible 

ew = over-water evaporation rate 

ew' = over-ice evaporation rate 

E = volumetric rate of evaporation from ice 

Eg = evapotranspiration from the groundwater zone storage 

El = evapotranspiration from the lower soil zone storage 

Es = evapotranspiration from the surface storage 

Eu = evapotranspiration from the upper soil zone storage 

εw = emissivity of water 

εa = emissivity of the atmosphere 

f = infiltration rate 

fk,m = ratio of surface temperature rise on day k from heat added on day m to that heat addition 

F = representing lake volume at which a heat addition is uniformly fully mixed, T > 3.98°C 

[evaporation model empirical parameter]

F' = representing lake volume at which a heat addition is uniformly fully mixed, T < 3.98°C 

[evaporation model empirical parameter]
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

76

GZM = content of groundwater zone 

γf = latent heat of fusion 

γv = latent heat of vaporization 

H = heat stored in the lake 

H' = heat stored in the ice pack 

Hs = nonlatent heat released to the atmosphere 

η = parameter relating cloudiness to atmospheric long-wave radiation [evaporation model empirical parameter]

K = units and proportionality constant 

LSZM = moisture content of lower soil zone 

m = daily snowmelt rate 

mp = daily potential snowmelt rate 

M = number of days in long-term heat balance 

Mk,m = mixing volume size on day k of heat added on day m 

n = number of days in the mass balance computation period 

ns = daily net supply rate to the watershed surface 

N = fraction of sky covered in clouds 

p = precipitation rate 

q = specific humidity of the air over the water 

q' = specific humidity of the air over the ice 

q0 = unit (per unit area) cloudless sky short-wave radiation rate 

qe = unit evaporative (latent and advected) heat transfer rate 

qe' = unit evaporative (latent and advected) heat transfer rate from ice pack 

qh = unit sensible heat transfer rate 

qh' = unit sensible heat transfer rate to ice pack 

qi = unit incident short-wave radiation rate 

qp = unit precipitation heat advection rate to water surface 

qp' = unit precipitation heat advection rate to ice pack 

qr = unit reflected short-wave radiation rate 

qr' = unit reflected short-wave radiation rate to ice pack 

qw = specific humidity of saturated air at temperature of water 

qw' = specific humidity of saturated air at temperature of ice 

q↑ = long-wave radiation emitted by the water body 

q↓ = long-wave radiation from the atmosphere absorbed by the water surface 

Q = basin outflow volume for n days 

Qa = heat flux between atmosphere and ice pack used for freezing or melting 

Ql = net long-wave radiation exchange rate 

Qw = total heat flux between the water body and the ice pack 

QI = net heat advection to the lake from surface flows 

Θi = sum of all surface inflows to lake 

Θo = sum of all outflows from lake 

ra = reflectivity of the water surface 

rr = daily solar insolation at the watershed surface 

ρ = density of ice 

ρa = density of air 

ρw = density of water 

S = volumetric rate of snow falling on ice 

SNW = water content of the snowpack 
GREAT LAKES CLIMATE CHANGE HYDROLOGIC IMPACT ASSESSMENT 

IJC LAKE ONTARIO—ST. LAWRENCE RIVER STUDY 

77

SS = content of surface storage zone 

σ = Stephan-Bolzmann constant 

t = time 

T = water surface temperature 

T' = ice surface temperature 

Ta = air temperature 

Ta' = over-ice air temperature 

Tb = a base scaling temperature [runoff model empirical parameter]

Tmax = maximum daily air temperature 

Tmin = minimum daily air temperature 

τ = daily extra-terrestrial solar radiation 

τa = parameter reflecting ice pack shape, vertical-lateral change ratios along atmosphere-ice boundary, and ice buoyancy [evaporation model empirical parameter]

τw = parameter reflecting ice pack shape, vertical-lateral change ratios along water-ice boundary, 

and ice buoyancy [evaporation model empirical parameter]

U = wind speed over water 

USZC = capacity of the upper soil zone (= 2 cm) 

USZM = moisture content of upper soil zone 

V = volume of the ice pack 

V' = volume of ice formed by only by freezing or melting 

Vc = lake volume (capacity) 

Ve = equilibrium lake volume approached as a limit by mixing [evaporation model empirical parameter]

W = daily wind movement 

X = ratio of hours of bright sunshine to maximum possible 

Ψ = total heat available for evapotranspiration during the day 

Z = volume of water in storage